Reserve for Unpaid Losses and Loss Adjustment Expenses - GB Liabilities for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning liabilities for unpaid losses and loss adjustment expenses, gross	$ 36,517
Less: payments
Ending liabilities for unpaid losses and loss adjustment expenses, gross	36,870
Group Insurance Policy [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning liabilities for unpaid losses and loss adjustment expenses, gross	8,256	$ 8,445
Reinsurance recoverables [1]	244	234		$ 246	$ 239
Beginning liabilities for unpaid losses and loss adjustment expenses, net	8,010	8,206
Provision for unpaid losses and loss adjustment expense
Current incurral year	2,297	2,269
Prior year's discount accretion	111	117
Prior incurral year development [2]	(315)	(206)
Total provision for unpaid losses and loss adjustment expenses	2,093	2,180
Less: payments
Current incurral year	(871)	(922)
Prior incurral years	(1,290)	(1,342)
Total payments	(2,161)	(2,264)
Ending liabilities for unpaid losses and loss adjustment expenses, net	7,942	8,122
Ending liabilities for unpaid losses and loss adjustment expenses, gross	8,186	8,356
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	$ 89	$ 85
Cumulative Effect, Period of Adoption, Adjustment [Member] | Reinsurance Recoverable Including Reinsurance Premium Paid [Member] | Accounting Standards Update 2016-13 [Member] | Group Insurance Policy [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Reinsurance recoverables [1]			$ (1)