Reserve for Unpaid Losses and Loss Adjustment Expenses - GB Liabilities for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning liabilities for unpaid losses and loss adjustment expenses, gross	$ 41,243
Less: payments
Ending liabilities for unpaid losses and loss adjustment expenses, gross	41,686
Group Insurance Policy [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning liabilities for unpaid losses and loss adjustment expenses, gross	8,160	$ 8,210
Reinsurance recoverables	243	251	$ 245	$ 245
Beginning liabilities for unpaid losses and loss adjustment expenses, net	7,915	7,965
Provision for unpaid losses and loss adjustment expense
Current incurral year	3,899	3,665
Prior year's discount accretion	149	156
Prior incurral year development [1]	(403)	(323)
Total provision for unpaid losses and loss adjustment expenses	3,645	3,498
Less: payments
Current incurral year	(1,772)	(1,703)
Prior incurral years	(1,798)	(1,900)
Total payments	(3,570)	(3,603)
Liability for Unpaid Claims and Claims Adjustment Expense, Net	7,990	7,860	7,915	7,965
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	(243)	(251)	$ (245)	$ (245)
Ending liabilities for unpaid losses and loss adjustment expenses, gross	8,233	8,111
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	$ 136	$ 138