Reserve for Unpaid Losses and Loss Adjustment Expenses - GB Liabilities for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	9 Months Ended		16 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 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	37,306		$ 37,306
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]			242		$ 246	$ 231	$ 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	3,339	3,351
Prior year's discount accretion	160	169
Prior incurral year development [2]	(362)	(321)
Total provision for unpaid losses and loss adjustment expenses	3,137	3,199
Less: payments
Current incurral year	(1,553)	(1,603)
Prior incurral years	(1,681)	(1,743)
Total payments	(3,234)	(3,346)
Beginning liabilities for unpaid losses and loss adjustment expenses, net	8,010	8,206	7,913		$ 8,010	$ 8,059	$ 8,206
Ending liabilities for unpaid losses and loss adjustment expenses, gross	8,155	8,290	$ 8,155
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	$ 133	$ 130
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)