Business, Basis of Presentation and Significant Accounting Policies Narrative (Details) - USD ($) $ in Millions	Jan. 01, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Cumulative-effect adjustment that decreased retained earnings		$ 17,117	$ 15,639	$ 14,141	$ 13,545	$ 12,365	$ 8,276
Available-for-sale securities		69,160		67,479
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect adjustment that decreased retained earnings				(125)
RMBS
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Available-for-sale securities		6,434		6,872
RMBS | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Available-for-sale securities	$ 17
Commercial mortgage loans
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Mortgage loans, before allowance for credit losses		11,390		10,515
Commercial mortgage loans | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Mortgage loans, before allowance for credit losses	$ 36
Retained earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect adjustment that decreased retained earnings		$ 7,010	$ 6,437	6,939	$ 6,668	$ 6,461	$ 5,286
Retained earnings | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect adjustment that decreased retained earnings				$ (117)
New accounting pronouncement effect, percentage	1.59%