Allowance for Expected Credit Losses (Details) - Changes in the Allowance for Expected Credit Losses on Premiums Receivable - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Credit Loss [Abstract]
Premiums receivable (net of allowance for expected credit losses), balance, beginning of period	$ 9,132	$ 8,555	$ 8,085	$ 7,829
Premiums receivable (net of allowance for expected credit losses), balance, end of period	8,886	8,289	8,886	8,289
Premiums receivable, allowance for expected credit losses [Roll Forward]
Premiums receivable, allowance for expected credit losses, beginning balance	89	105	107	105
Current period change for expected credit losses	14	15	49	45
Write-offs of uncollectible premiums receivable	17	18	70	48
Premiums receivable, allowance for expected credit losses, ending balance	$ 86	$ 102	$ 86	$ 102