Allowance for Expected Credit Losses - Premiums receivable (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2024	Dec. 31, 2023
Credit Loss [Abstract]
Balance at beginning of period		$ 4,644	$ 3,625
Balance at end of period		5,634	4,644
Allowance for Expected Credit Losses
Balance at beginning of period		34	35
Provision on business acquired	[1]	16
Change for provision of expected credit losses	[2]	(5)	(1)
Balance at end of period		45	34
Write-offs charged against the allowance		$ 3	$ 3

[1] Reflects provision for current expected credit losses on premiums receivable related to the MCE Acquisition.

[2] Amounts deemed uncollectible are written-off in operating expenses. For the 2024 and 2023 periods, amounts written off totaled $3 million and $3 million, respectively.