Allowance for Expected Credit Losses (Details) - Changes in the Allowance for Expected Credit Losses on Premiums Receivable - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
|
| Credit Loss [Abstract] | ||
| Premiums receivable (net of allowance for expected credit losses), balance, beginning of period | $ 10,992 | $ 11,110 |
| Premiums receivable (net of allowance for expected credit losses), balance, end of period | 11,423 | 11,575 |
| Premiums receivable, allowance for expected credit losses [Roll Forward] | ||
| Premiums receivable, allowance for expected credit losses, beginning balance | 58 | 58 |
| Current period change for expected credit losses | 18 | 16 |
| Write-offs of uncollectible premiums receivable | 16 | 16 |
| Premiums receivable, allowance for expected credit losses, ending balance | $ 60 | $ 58 |