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, 2025 |
Jun. 30, 2024 |
Jun. 30, 2025 |
Jun. 30, 2024 |
|
| Credit Loss [Abstract] | ||||
| Premiums receivable (net of allowance for expected credit losses), balance, beginning of period | $ 11,575 | $ 10,829 | $ 11,110 | $ 10,282 |
| Premiums receivable (net of allowance for expected credit losses), balance, end of period | 12,042 | 11,491 | 12,042 | 11,491 |
| Premiums receivable, allowance for expected credit losses [Roll Forward] | ||||
| Premiums receivable, allowance for expected credit losses, beginning balance | 58 | 68 | 58 | 69 |
| Current period change for expected credit losses | 19 | 13 | 35 | 25 |
| Write-offs of uncollectible premiums receivable | 16 | 12 | 32 | 25 |
| Premiums receivable, allowance for expected credit losses, ending balance | $ 61 | $ 69 | $ 61 | $ 69 |