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, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Credit Loss [Abstract]
Premiums receivable (net of allowance for expected credit losses), balance, beginning of period	$ 9,483	$ 8,593	$ 8,922	$ 8,085
Premiums receivable (net of allowance for expected credit losses), balance, end of period	10,327	9,132	10,327	9,132
Premiums receivable, allowance for expected credit losses [Roll Forward]
Premiums receivable, allowance for expected credit losses, beginning balance	77	89	77	107
Current period change for expected credit losses	7	17	17	35
Write-offs of uncollectible premiums receivable	12	17	22	53
Premiums receivable, allowance for expected credit losses, ending balance	$ 72	$ 89	$ 72	$ 89