Allowance for Expected Credit Losses (Details) - Changes in the Allowance for Expected Credit Losses on Premiums Receivable - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 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	10,282	8,922
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	42	54
Write-offs of uncollectible premiums receivable	50	84
Premiums receivable, allowance for expected credit losses, ending balance	$ 69	$ 77