| Cumulative Cost Basis | $113.5B | $119.4B | $115.1B | $114.9B | $118.9B | $123.7B | $124.7B | $127.3B |
| Total | $113.5B | $119.4B | $115.1B | $114.9B | $118.9B | $123.7B | $124.7B | $127.3B |
| Available for sale investments | $107.8B | $117.3B | $110.4B | $111.1B | $116.1B | $121.8B | $122.7B | $123.4B |
| Liability for Unpaid Claims and Claims Adjustment Expense, Net | $64.8B | $66.7B | $66.3B | $67.4B | $68.7B | $70.0B | $69.7B | $70.7B |
| Debt Securities, Available-for-Sale, Unrealized Loss Position | $70.0B | $49.4B | $67.7B | $60.5B | $49.0B | $44.2B | $44.9B | $66.3B |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five | $34.1B | $35.7B | $33.4B | $33.3B | $36.2B | $36.3B | $35.6B | $36.3B |
| Less than 12 months | $17.4B | $3.9B | $28.0B | $21.9B | $12.8B | $9.4B | $12.6B | $36.3B |
| Stated Maturities | $24.6B | $28.5B | $27.2B | $27.5B | $28.5B | $30.2B | $30.7B | $31.3B |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 | $26.8B | $28.9B | $26.9B | $27.0B | $27.6B | $30.5B | $31.5B | $31.1B |
| 12 months or more | $52.6B | $45.5B | $39.8B | $38.7B | $36.2B | $34.8B | $32.4B | $30.0B |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 | $17.6B | $19.6B | $18.3B | $18.3B | $18.6B | $19.6B | $20.1B | $20.2B |
| Restricted assets in fixed maturities and short-term investments | $18.4B | $19.5B | $17.9B | $18.1B | $18.3B | $19.1B | $19.0B | $19.4B |
| Reinsurance recoverable on unpaid losses and loss expenses | $17.4B | $17.6B | $17.7B | $18.1B | $17.7B | $18.4B | $18.3B | $18.3B |
| Carrying value of limited partnerships and partially-owned investment companies included in other investments | $14.1B | $14.2B | $14.5B | $15.3B | $16.0B | $16.4B | $16.9B | $16.8B |
| Policyholder Account Balance, excluding Unearned Revenue Liability | $6.6B | $6.9B | $6.7B | $6.8B | $7.0B | $7.2B | $7.2B | $7.4B |
| Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments | $6.8B | $6.8B | $6.4B | $6.4B | $6.9B | $6.4B | $7.2B | $7.3B |
| Separate Account, Liability, Cash Surrender Value, Amount | $5.6B | $5.8B | — | $5.9B | $6.1B | $6.3B | — | $6.2B |
| Noncontrolling interests in subsidiaries | $3.5B | $4.4B | $4.4B | $5.0B | $5.1B | $6.0B | $6.0B | $6.1B |
| Short-term investments, amortized cost | $4.5B | $4.4B | $5.1B | $4.4B | $4.5B | $4.4B | $4.8B | $5.1B |
| Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax | $6.4B | $4.1B | $5.8B | $5.0B | $4.5B | $3.9B | $3.9B | $4.8B |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One | $4.7B | $4.5B | $4.5B | $4.9B | $5.2B | $5.2B | $4.7B | $4.6B |
| Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss | $5.1B | $3.3B | $4.7B | $4.1B | $3.5B | $3.2B | $3.1B | $4.1B |
| Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | $4.9B | $3.3B | $4.2B | $3.8B | $3.3B | $3.0B | $2.9B | $3.3B |
| Securities lending collateral | — | — | — | — | — | — | $2.5B | $2.3B |
| Reinsurance recoverable on paid losses and loss expenses | $1.9B | $2.0B | $2.0B | $1.9B | $1.9B | $1.8B | $2.0B | $1.9B |
| Deferred income taxes | $1.6B | $1.7B | $1.6B | $1.6B | $1.7B | $1.7B | $1.7B | $1.8B |
| Gross Unrealized Gains | $823.0M | $2.0B | $1.1B | $1.3B | $1.7B | $2.0B | $2.0B | $1.0B |
| Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | $226.0M | $45.0M | $518.0M | $334.0M | $201.0M | $166.0M | $237.0M | $776.0M |
| Unearned Revenue Liability | $675.0M | $712.0M | $711.0M | $719.0M | $753.0M | $760.0M | $758.0M | $762.0M |
| Policyholder Account Balance, Other Reconciling Items | $500.0M | $556.0M | — | $566.0M | $577.0M | $578.0M | — | $603.0M |
| goodwill attributable to noncontrolling interests | $500.0M | $509.0M | — | — | $456.0M | $460.0M | — | $420.0M |
| Common stock, shares authorized (in shares) | — | — | — | — | — | — | 412.1M | 400.1M |
| Common stock, shares issued (in shares) | 419.6M | 419.6M | 419.6M | 412.1M | 412.1M | 412.1M | 412.1M | 400.1M |
| Common Stock, Shares, Outstanding | 404.1M | 403M | 400.7M | 400.7M | 398.7M | 394.3M | 391.1M | 388.5M |
| Valuation allowance for uncollectible reinsurance | $381.0M | $388.0M | $310.0M | $320.0M | $323.0M | $326.0M | $320.0M | $320.0M |
| Reinsurance Recoverables on Unpaid Losses, Allowance | $299.0M | $307.0M | $242.0M | $254.0M | $261.0M | $265.0M | $248.0M | $256.0M |
| Derivative Liability, Subject to Master Netting Arrangement, after Offset | $103.0M | $139.0M | $199.0M | $223.0M | $87.0M | $84.0M | $179.0M | $112.0M |
| Variable Interest Entity, Nonconsolidated, Comparison of Carrying Amount of Assets and Liabilities to Maximum Loss Exposure | $215.0M | $110.0M | $97.0M | $89.0M | $110.0M | $159.0M | $70.0M | $89.0M |
| Reinsurance Recoverables on Paid Losses, Allowance | $82.0M | $81.0M | $68.0M | $66.0M | $62.0M | $61.0M | $72.0M | $64.0M |
| Insurance and reinsurance balances receivable, valuation allowance | $54.0M | $58.0M | $59.0M | $58.0M | $55.0M | $60.0M | $62.0M | $63.0M |
| Debt Securities, Available-for-Sale, Allowance for Credit Loss | $122.0M | $75.0M | $70.0M | $63.0M | $71.0M | $50.0M | $52.0M | $50.0M |
| Treasury stock, shares (in shares) | 15.6M | 16.6M | 18.9M | 11.4M | 13.4M | 17.8M | 21M | 11.6M |
| Common stock, par value (in dollars per share) | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 |
| Annual dividend per share approved by shareholders | $3.88 | — | — | — | $3.88 | — | — | — |
| Common Stock, Dividend Rate Approved | $0.97 | — | — | — | $0.97 | — | — | — |
| Reinsurance Recoverables on Future Policy Benefits, Allowance | $0.0 | $0.0 | $0.0 | $0.0 | $0.0 | $0.0 | $0.0 | $0.0 |
