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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Credit Loss [Abstract]
Premiums receivable (net of allowance for expected credit losses), balance, beginning of period	$ 8,593	$ 8,167	$ 8,085	$ 7,829
Premiums receivable (net of allowance for expected credit losses), balance, end of period	9,132	8,555	9,132	8,555
Premiums receivable, allowance for expected credit losses [Roll Forward]
Premiums receivable, allowance for expected credit losses, beginning balance	89	110	107	105
Current period change for expected credit losses	17	14	35	30
Write-offs of uncollectible premiums receivable	17	19	53	30
Premiums receivable, allowance for expected credit losses, ending balance	$ 89	$ 105	$ 89	$ 105