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, 2024	Mar. 31, 2023
Credit Loss [Abstract]
Premiums receivable (net of allowance for expected credit losses), balance, beginning of period	$ 10,282	$ 8,922
Premiums receivable (net of allowance for expected credit losses), balance, end of period	10,829	9,483
Premiums receivable, allowance for expected credit losses [Roll Forward]
Premiums receivable, allowance for expected credit losses, beginning balance	69	77
Current period change for expected credit losses	12	10
Write-offs of uncollectible premiums receivable	13	10
Premiums receivable, allowance for expected credit losses, ending balance	$ 68	$ 77