| Debt Securities, Available-for-Sale, Amortized Cost, after Allowance for Credit Loss | $24.5B | $26.4B | $26.6B | $26.3B | $26.7B | $27.7B | $28.6B | $28.6B |
| Available for sale investments | $23.8B | $26.5B | $26B | $26B | $26.6B | $27.8B | $28.7B | $28.4B |
| Liability for Unpaid Claims and Claims Adjustment Expense, Net | $13.9B | $14.5B | $15B | $14.6B | $14.3B | $15.3B | $15.3B | $15.4B |
| Vendor and manufacturer receivables | $13.5B | $15.6B | $13.9B | $14.2B | $15.2B | $17.8B | $15.6B | $14.1B |
| Debt Securities, Available-for-Sale, Unrealized Loss Position | $15B | $7.5B | $13.2B | $9.9B | $6.6B | $5.4B | $6.3B | $12.8B |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five | $8.8B | $10.5B | — | $10.7B | $11.1B | $11.5B | — | $11.5B |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five | $9B | $10.5B | — | $10.7B | $11B | $11.4B | — | $11.5B |
| Incurred but not reported (IBNR) claims liability, net | $10.6B | $11B | — | $10.7B | $10.4B | $10.6B | — | $10.6B |
| Less than 12 months | $6B | $871M | $7.5B | $4.9B | $2.5B | $1.8B | $2.9B | $10.1B |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 | $4.4B | $4.8B | — | $4.4B | $4.5B | $4.7B | — | $5.7B |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 | $4.3B | $4.9B | — | $4.4B | $4.6B | $4.8B | — | $5.7B |
| Deferred income taxes | $4.1B | $3.6B | $3.8B | $3.7B | $3.6B | $3.5B | $3.8B | $3.8B |
| Common stock, shares authorized (in shares) | 3.2B | 3.2B | 3.2B | 3.2B | 3.2B | 3.2B | 3.2B | 3.2B |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10 | $3.6B | $3.1B | — | $2.9B | $2.8B | $2.8B | — | $3.1B |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 | $3.3B | $3.1B | — | $2.7B | $2.6B | $2.7B | — | $2.9B |
| 12 months or more | $9B | $6.6B | $5.7B | $5B | $4.1B | $3.7B | $3.5B | $2.7B |
| Less: current maturities | $3.7B | $4.9B | $3.6B | $4.4B | $6.2B | $4.1B | $4.1B | $2.6B |
| Common stock, shares issued (in shares) | 1.8B | 1.8B | 1.8B | 1.8B | 1.8B | 1.8B | 1.8B | 1.8B |
| Common Stock, Shares, Outstanding | 1.3B | 1.3B | 1.3B | 1.3B | 1.3B | 1.3B | 1.3B | 1.3B |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One | $1.3B | $816M | — | $1.2B | $963M | $838M | — | $852M |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One | $1.4B | $819M | — | $1.2B | $961M | $835M | — | $850M |
| Treasury stock, shares (in shares) | 521M | 519M | 518M | 517M | 518M | 516M | 516M | 515M |
| Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax | $863M | $453M | $707M | $547M | $449M | $332M | $331M | $447M |
| Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss | $863M | $453M | $707M | $547M | $449M | $332M | $331M | $447M |
| Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | $799M | $446M | $580M | $476M | $396M | $307M | $301M | $305M |
| Gross Unrealized Gains | $146M | $510M | $178M | $246M | $347M | $462M | $449M | $245M |
| Accounts Receivable, Allowance for Credit Loss | $355M | $346M | $407M | $392M | $374M | $178M | $182M | $200M |
| Noncontrolling interests in subsidiaries | $181M | $162M | $170M | $181M | $172M | $182M | $168M | $181M |
| Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | $64M | $7M | $127M | $71M | $53M | $25M | $30M | $142M |
| Reinsurance recoverable on unpaid losses and loss expenses | $59M | $65M | $81M | $114M | $103M | $94M | $90M | $132M |
| Number of pharmacy plan members | 90000000.00 | 90000000.00 | — | 88000000.00 | 87000000.00 | 87000000.00 | — | 88000000.00 |
| Treasury shares held in trust | $29M | $29M | $29M | $29M | $29M | $29M | $29M | $29M |
| Effect of changes in discount rate assumptions | $24M | $19M | $1M | -$2M | $30M | $24M | $20M | $18M |
| Gains expected to be reclassified | — | — | — | $16M | $16M | $16M | — | $16M |
| Treasury shares held in trust (in shares) | 1M | 1M | 1M | 1M | 1M | 1M | 1M | 1M |
| Preferred Stock, Shares Authorized | 100K | 100K | 100K | 100K | 100K | 100K | 100K | 100K |
| Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions | 9729.00 | 5047.00 | 8676.00 | 6723.00 | 4596.00 | 3785.00 | 4043.00 | 7287.00 |
| Number of Securities, Greater than 12 months | 6232.00 | 4554.00 | 4174.00 | 3711.00 | 3068.00 | 2675.00 | 2465.00 | 2019.00 |
| Guarantor obligations, number of leases | 62.00 | 61.00 | — | 60.00 | 60.00 | 60.00 | — | 59.00 |
| Common stock, par value (in dollars per share) | $0.01 | $0.01 | $0.01 | $0.01 | $0.01 | $0.01 | $0.01 | $0.01 |
| Preferred Stock, Par or Stated Value Per Share | $0.01 | $0.01 | $0.01 | $0.01 | $0.01 | $0.01 | $0.01 | $0.01 |
| Debt Securities, Available-for-Sale, Allowance for Credit Loss | $0 | $0 | $0 | $0 | $0 | $0 | $0 | $0 |
| Financial Liabilities Fair Value Disclosure | — | — | — | — | — | — | $0 | $0 |
| Preferred Stock, Shares Issued | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Preferred Stock, Shares Outstanding | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Premium deficiency reserve | $0 | $670M | — | $431M | $902M | $728M | — | $0 |
