Reserve for Unpaid Losses and Loss Adjustment Expenses - GB Liabilities for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning liabilities for unpaid losses and loss adjustment expenses, gross	$ 42,318
Ending liabilities for unpaid losses and loss adjustment expenses, gross	42,771
Group Insurance Policy [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning liabilities for unpaid losses and loss adjustment expenses, gross	8,274	$ 8,160
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	(255)	(248)	$ (254)	$ (245)
Ending liabilities for unpaid losses and loss adjustment expenses, gross	7,979	7,936	$ 8,020	$ 7,915
Ending liabilities for unpaid losses and loss adjustment expenses, gross	8,234	8,184
Provision for unpaid losses and loss adjustment expense
Current incurral year	1,376	1,325
Prior year's discount accretion	53	53
Prior incurral year development [1]	(189)	(133)
Total provision for unpaid losses and loss adjustment expenses	1,240	1,245
Less: payments
Current incurral year	(357)	(335)
Prior incurral years	(924)	(889)
Total payments	(1,281)	(1,224)
Group Insurance Policy [Member] | Other Operating Income (Expense) [Member]
Provision for unpaid losses and loss adjustment expense
Total provision for unpaid losses and loss adjustment expenses	$ 45	$ 45