Reinsurance, Allowance (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Reinsurance Disclosures [Abstract]
Valuation allowance for uncollectible reinsurance - beginning of period	$ 367	$ 351
Provision for uncollectible reinsurance	8	5
Write-offs charged against the valuation allowance	0	(5)
Valuation allowance for uncollectible reinsurance - end of period	$ 375	$ 351