Reinsurance, Allowance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reinsurance Disclosures [Abstract]
Valuation allowance for uncollectible reinsurance	$ 367	$ 351	$ 329
Provision for uncollectible reinsurance	47	43
Write-offs charged against the valuation allowance	(32)	(19)
Foreign exchange revaluation	$ 1	$ (2)