Derivatives (Estimated Fair Value of Derivatives Assets and Liabilities after Master Netting Agreements and Cash Collateral) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Offsetting Derivative Assets [Abstract]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	$ 2,363	$ 3,113
Derivative Asset, Not Offset, Policy Election Deduction	(1,321)	(1,155)
Derivative Asset, Collateral, Obligation to Return Cash, Offset	(837)	(1,480)
Derivative Asset, Fair Value, Amount Offset Against Collateral	205	478
Derivative Asset, Collateral, Obligation to Return Securities, Offset	(188)	(413)
Derivative Asset, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	17	65
Offsetting Derivative Liabilities [Abstract]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	1,854	1,632
Derivative Liability, Not Offset, Policy Election Deduction	(1,321)	(1,155)
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	533	477
Derivative Liability, Collateral, Right to Reclaim Securities, Offset	(533)	(477)
Derivative Liability, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	$ 0	$ 0