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, 2024 |
Jun. 30, 2023 |
Jun. 30, 2024 |
Jun. 30, 2023 |
|
| Credit Loss [Abstract] | ||||
| Premiums receivable (net of allowance for expected credit losses), balance, beginning of period | $ 10,829 | $ 9,483 | $ 10,282 | $ 8,922 |
| Premiums receivable (net of allowance for expected credit losses), balance, end of period | 11,491 | 10,327 | 11,491 | 10,327 |
| Premiums receivable, allowance for expected credit losses [Roll Forward] | ||||
| Premiums receivable, allowance for expected credit losses, beginning balance | 68 | 77 | 69 | 77 |
| Current period change for expected credit losses | 13 | 7 | 25 | 17 |
| Write-offs of uncollectible premiums receivable | 12 | 12 | 25 | 22 |
| Premiums receivable, allowance for expected credit losses, ending balance | $ 69 | $ 72 | $ 69 | $ 72 |