Reserve for Unpaid Losses and Loss Adjustment Expenses - GB Liabilities for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	3 Months Ended		22 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning liabilities for unpaid losses and loss adjustment expenses, gross	$ 37,855
Less: payments
Ending liabilities for unpaid losses and loss adjustment expenses, gross	38,540		$ 38,540
Group Insurance Policy [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning liabilities for unpaid losses and loss adjustment expenses, gross	8,233	$ 8,256
Reinsurance recoverables [1]			247	$ 237	$ 249		$ 246
Beginning liabilities for unpaid losses and loss adjustment expenses, net	7,996	8,010
Provision for unpaid losses and loss adjustment expense
Current incurral year	1,325	1,148
Prior year's discount accretion	55	57
Prior incurral year development [2]	(151)	(163)
Total provision for unpaid losses and loss adjustment expenses	1,229	1,042
Less: payments
Current incurral year	(350)	(278)
Prior incurral years	(914)	(821)
Total payments	(1,264)	(1,099)
Beginning liabilities for unpaid losses and loss adjustment expenses, net	7,996	8,010	7,961	$ 7,996	$ 7,953		$ 8,010
Ending liabilities for unpaid losses and loss adjustment expenses, gross	8,208	8,202	$ 8,208
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	$ 43	$ 44
Cumulative Effect, Period of Adoption, Adjustment [Member] | Reinsurance Recoverable Including Reinsurance Premium Paid [Member] | Group Insurance Policy [Member] | Accounting Standards Update 2016-13 [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Reinsurance recoverables [1]						$ (1)