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, 2023	Mar. 31, 2022
Credit Loss [Abstract]
Premiums receivable (net of allowance for expected credit losses), balance, beginning of period	$ 8,922	$ 8,085
Premiums receivable (net of allowance for expected credit losses), balance, end of period	9,483	8,593
Premiums receivable, allowance for expected credit losses [Roll Forward]
Premiums receivable, allowance for expected credit losses, beginning balance	77	107
Current period change for expected credit losses	10	18
Write-offs of uncollectible premiums receivable	10	36
Premiums receivable, allowance for expected credit losses, ending balance	$ 77	$ 89