Reinsurance, Allowance (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024
Reinsurance Disclosures [Abstract]
Valuation allowance for uncollectible reinsurance - beginning of period	$ 310	$ 367
Provision for uncollectible reinsurance	17	18
Write-offs charged against the valuation allowance	(6)	(3)
Foreign exchange revaluation	2	(1)
Valuation allowance for uncollectible reinsurance - end of period	$ 323	$ 381