Allowance for Expected Credit Losses (Details) - Changes in the Allowance for Expected Credit Losses on Premiums Receivable - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
|
| Credit Loss [Abstract] | ||||
| Premiums receivable (net of allowance for expected credit losses), balance, beginning of period | $ 11,423 | $ 11,575 | $ 10,992 | $ 11,110 |
| Premiums receivable (net of allowance for expected credit losses), balance, end of period | 12,382 | 12,042 | 12,382 | 12,042 |
| Premiums receivable, allowance for expected credit losses [Roll Forward] | ||||
| Premiums receivable, allowance for expected credit losses, beginning balance | 60 | 58 | 58 | 58 |
| Current period change for expected credit losses | 18 | 19 | 36 | 35 |
| Write-offs of uncollectible premiums receivable | 17 | 16 | 33 | 32 |
| Premiums receivable, allowance for expected credit losses, ending balance | $ 61 | $ 61 | $ 61 | $ 61 |