| Segment Reporting, Other Segment Item, Amount | — | — | — | — | — | — | $4.2B | $4.7B |
| Cash Provided by (Used in) Investing Activity, Including Discontinued Operation | -$1.6B | -$1.9B | -$2.5B | — | — | — | -$2.8B | -$3.4B |
| Capital Expenditures | $1.4B | $1.8B | $2.3B | — | — | — | $2.4B | $2.9B |
| Payments to Acquire Property, Plant, and Equipment | $1.4B | $1.8B | $2.3B | — | — | — | $2.4B | $2.9B |
| Proceeds from new debt | $700M | $1.5B | $1.6B | — | — | — | $4.6B | $2.4B |
| Depreciation, Amortization and Accretion, Net | $989M | $1B | $1.1B | — | — | — | $1.4B | $1.6B |
| Cash Provided by (Used in) Financing Activity, Including Discontinued Operation | -$193M | -$20M | $1.3B | — | — | — | $2.8B | $1.5B |
| Depreciation and amortization(b) | — | — | — | — | — | — | $1.3B | $1.4B |
| Comprehensive Income (Loss), Net of Tax, Attributable to Parent | — | $1.1B | $1.5B | — | — | $1.5B | $1.3B | $1.4B |
| Other Comprehensive Income (Loss) | — | $1.1B | $1.5B | — | — | $1.5B | $1.3B | $1.4B |
| Comprehensive Income Including Noncontrolling Interest | — | $1.1B | $1.5B | — | — | $1.5B | $1.3B | $1.3B |
| Comprehensive Income Attributable to Parent | — | $1.1B | $1.5B | — | — | $1.5B | $1.3B | $1.3B |
| Comprehensive Income Including Noncontrolling Interest | — | $1.1B | $1.5B | — | — | $1.5B | $1.3B | $1.3B |
| Comprehensive income (loss), including noncontrolling interest | — | $1.1B | $1.5B | — | — | $1.5B | $1.3B | $1.3B |
| Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest | — | $1.1B | $1.5B | — | — | $1.5B | $1.3B | $1.3B |
| Comprehensive Income (Loss), Total | — | $1.1B | $1.5B | — | — | $1.5B | $1.3B | $1.3B |
| Comprehensive Income, Including Noncontrolling Interest | — | $1.1B | $1.5B | — | — | $1.5B | $1.3B | $1.3B |
| Comprehensive Income Including Noncontrolling Interest | — | $1.1B | $1.5B | — | — | $1.5B | $1.3B | $1.3B |
| Total Comprehensive Income | — | $1.1B | $1.5B | — | — | $1.5B | $1.3B | $1.3B |
| Comprehensive Income | — | — | — | — | — | — | $1.3B | $1.3B |
| Repayment of Long-term Obligations | — | — | — | — | — | — | $35M | $1.3B |
| Repayment of Long-Term Debt, Long-Term Lease Obligation, and Capital Security | $977M | $874M | $81M | — | — | — | $35M | $1.3B |
| Cash Provided by (Used in) Operating Activity, Including Discontinued Operation | $1.6B | $2B | $1.4B | — | — | — | $1.3B | $1.2B |
| Capital investments accrued but not yet paid | $863M | — | $35M | — | — | — | $940M | $1B |
| Interest Paid, Net | $515M | $321M | $589M | — | — | — | $756M | $901M |
| Interest Paid, Excluding Capitalized Interest, Operating Activity | $515M | $321M | $589M | — | — | — | $756M | $901M |
| Dividends, Common Stock, Cash | $702M | $723M | $741M | $742M | $764M | $765M | $791M | $830M |
| Interest and Debt Expense | $462M | $488M | $511M | — | — | $620M | $714M | $778M |
| Payments of Ordinary Dividends, Common Stock | $702M | $723M | $741M | — | — | — | $736M | $776M |
| Cash Dividends, Common Stock | $702M | $723M | $741M | — | — | — | $736M | $776M |
| Net Change in Cash and Restricted Cash | — | — | — | — | — | — | $1.2B | -$653M |
| Increase (decrease) in notes payable, net | $137M | $126M | — | — | — | — | — | $653M |
| Accrued compensation | -$470M | — | — | — | — | — | -$537M | -$599M |
| Issuance of common stock in connection with the Spin-Off and reclassification of net parent investment | $38M | $23M | $1.7B | $15M | $7M | $4M | $85M | $589M |
| Accounts payable | $132M | $571M | $102M | — | — | — | -$394M | -$555M |
| Proceeds from Issuance of Common Stock | $38M | $23M | $1.7B | — | — | — | $30M | $535M |
| Taxes other than income taxes and other – net | $372M | $349M | $352M | — | — | $341M | $445M | $464M |
| Payments to Acquire Investments to be Held in Decommissioning Trust Fund | — | — | $230M | — | — | — | $361M | $442M |
| Proceeds from Decommissioning Trust Fund Assets | $289M | $335M | $230M | — | — | — | $361M | $442M |
| Increase (Decrease) in Energy Related Inventory, Natural Gas in Storage | -$450M | — | $471M | — | — | — | -$365M | -$355M |
| Proceeds from other short-term debt | $850M | $350M | — | — | — | — | $0 | $350M |
| Construction payables | $23M | — | — | — | — | — | -$161M | -$251M |
| Financing — other | -$115M | -$104M | -$16M | — | — | — | -$133M | -$191M |
| Increase Decrease In Interest Payable Net | -$128M | — | — | — | — | — | -$82M | -$180M |
| Deferred taxes | $40M | $200M | $368M | — | — | — | $351M | $168M |
| Payments for Removal Costs | $227M | $150M | $141M | — | — | — | $168M | $166M |
| Other income, net (Note 6) | $145M | $139M | $132M | — | — | $141M | $149M | $155M |
| Asset Retirement Obligation Payments | — | — | — | — | — | — | $134M | $133M |
| Asset Retirement Obligation Cash Paid To Settle | $87M | $111M | $116M | — | — | — | $134M | $133M |
| Allowance for Funds Used During Construction, Equity | $51M | $53M | $59M | — | — | $66M | $73M | $121M |
| Lease Income | — | $188M | $196M | — | — | $176M | $120M | $118M |
| Increase (Decrease) in Prepaid Expense | $86M | $4M | — | — | — | — | $120M | $98M |
| Storm Damage Cost Recovery, Noncurrent | — | — | — | — | — | — | $173M | $93M |
| Increase (Decrease) in Materials and Supplies | $28M | $81M | $29M | — | — | — | -$11M | $85M |
| Variable lease income | — | $129M | $139M | — | — | $134M | $81M | $79M |
| Increase (Decrease) Retail Fuel Cost Under Recovery Short Term | — | — | — | — | — | — | -$71M | -$63M |
| Other investing activities, net | — | — | — | — | — | — | $68M | $60M |
| Payment for (Proceeds from) Other Investing Activity | -$110M | — | $159M | — | — | — | $68M | $60M |
| Common Stock Issued for Business Acquisition | — | — | — | — | — | — | $55M | $54M |
| Repayments of Other Short-Term Debt | $100M | $300M | $500M | — | — | — | $0 | $50M |
| Payments to Noncontrolling Interests | — | — | — | — | — | — | $37M | $47M |
| Minority Interest Decrease From Distributions To Noncontrolling Interest Holders | $98M | $28M | $57M | $48M | $42M | $59M | $37M | $46M |
| Increase (decrease) in fair value of funds | — | -$230M | -$106M | — | — | -$4M | -$6M | -$44M |
| ROU Asset Obtained - Operating Lease | — | — | — | — | — | — | $87M | $41M |
| Lease income — operating leases | — | $52M | $50M | — | — | $36M | $33M | $34M |
| Forward Contract Indexed To Issuers Equity Shares | — | — | — | — | — | — | — | 27.4M |
| Increase (Decrease) in Other Operating Assets | -$87M | — | $322M | — | — | — | -$66M | $27M |
| Increase (Decrease) in over Energy Recovery | — | — | — | — | — | — | $179M | $27M |
| Other Noncash Income (Expense) | -$7M | -$14M | $140M | — | — | — | $1M | $25M |
| OCI Attributable to Noncontrolling Interest | — | -$22M | $12M | — | — | $10M | -$64M | -$18M |
| Less: comprehensive income attributable to noncontrolling interest | — | -$22M | $12M | — | — | $10M | -$64M | -$18M |
| Net Income Loss Attributable To Noncontrolling Interest | — | -$22M | $12M | — | — | $10M | -$64M | -$18M |
| Comprehensive Income Attributable to Noncontrolling Interests | — | -$22M | $12M | — | — | $10M | -$64M | -$18M |
| Comprehensive Income, Noncontrolling Interest | — | -$22M | $12M | — | — | $10M | -$64M | -$18M |
| Expected Volume of Natural Gas Subject to Option to Sell Back Excess Gas Due to Operational Constraints | — | — | — | — | — | — | — | 13000000.00 |
| Share-based compensation expense related to employee stock plans | $6M | $14M | $15M | $29M | $19M | $7M | $5M | -$9M |
| Extinguishment Of Debt Gain Loss Net Of Tax | — | — | — | — | — | — | — | -$8M |
| Amortization of capitalized software and acquired intangible assets | — | $9M | $11M | — | — | $10M | $8M | $7M |
| Decrease in operating revenues | — | $5M | $14M | — | — | $5M | $5M | $5M |
| Customer refunds | — | — | — | — | — | — | -$95M | $5M |
| Sales-type Lease, Interest Income | — | $7M | $7M | — | — | $6M | $6M | $5M |
| Change in Other Liabilities | $35M | — | -$112M | — | — | — | -$37M | -$4M |
| Other liabilities | $35M | — | -$112M | — | — | — | -$37M | -$4M |
| Add - Incremental shares under stock-based compensation plans (in shares) | — | $5M | $6M | — | — | $7M | $5M | $4M |
| Noncontrolling Interest, Increase from Contributions from Noncontrolling Interest Holders | $73M | — | — | $21M | — | — | $19M | $4M |
| Cash Flow Hedge Reclassification, After Tax | — | -$54M | -$26M | — | — | -$36M | $12M | -$4M |
| Net gains (losses) deferred | — | -$45M | $0 | — | — | $2M | $14M | -$3M |
| Stockholders' Equity, Other | -$7M | -$2M | $8M | $0 | $0 | $1M | $5M | $3M |
| OCI Cash Flow Hedge After Reclassification Before Tax | — | -$61M | $2M | — | — | $5M | $20M | -$3M |
| Stockholders' Equity, Other | — | — | — | — | — | — | $5M | $3M |
| ROU Asset Obtained - Finance Lease | — | — | — | — | — | — | $13M | $2M |
| Other comprehensive income (loss), after-tax | — | — | — | — | — | — | $3M | $2M |
| Other comprehensive income (loss) | — | $11M | $28M | — | — | $38M | $3M | $2M |
| Right Of Use Asset Obtained In Exchange For Finance Lease Liability | — | — | — | — | — | — | $13M | $2M |
| Tax effect of unrealized gain (loss) on cash flow hedges | — | -$17M | -$8M | — | — | -$12M | $4M | -$1M |
| Unrealized Gain (Loss) on Derivatives, Net | — | -$15M | $2M | — | — | $3M | $5M | -$1M |
| Cash Flow Hedge Reclassification, Tax | — | -$17M | -$8M | — | — | -$12M | $4M | -$1M |
| Recognition of Net Gains/Losses on Benefit Obligations, Net of Taxes | — | — | — | — | — | — | $1M | $1M |
| Tax on Reclassification of Hedging Instruments | — | -$17M | -$8M | — | — | -$12M | $4M | -$1M |
| Amortization of Actuarial Gain, Net of Tax | — | — | — | — | — | — | $1M | $1M |
| Common Stock Dividends Per Share (Paid) | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 |
| Common stock dividends per share cash paid | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 |
| Common Stock Dividends Per Share (Cash Paid) | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 |
| Common Dividends Per Share Paid | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 |
| Cash Dividend per Common Share | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 | $0.7 |
| Effective tax rates | — | — | $0 | — | — | — | $0.2 | $0.1 |
| Income Taxes Paid, Net | -$8M | $165M | $3M | — | — | — | -$1M | $0 |
| Income Taxes Paid, Net | -$8M | $165M | $3M | — | — | — | -$1M | $0 |
| Repayments of Notes Payable | — | — | — | — | — | — | $841M | — |
| Recognition of Net Gains/Losses on Benefit Obligations, Tax Provision | — | — | — | — | — | — | $0 | $0 |
