Derivative Instruments and Hedging Activities (Statement of Gains and Losses on Derivative Instruments Reported in Statement of Comprehensive Income) (Details) - Not designated as hedging instrument - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments recognized in earnings	$ (8)	$ (28)	$ (25)	$ (35)
Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments recognized in earnings	1	(23)	(6)	(38)
Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments recognized in earnings	(2)	(5)	(4)	3
Other credit derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments recognized in earnings	(7)	0	(15)	0
Loss on mortgage and automotive loans | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments recognized in earnings	(1)	0	(8)	(15)
Other income, net of losses | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments recognized in earnings	2	(23)	2	(23)
Other income, net of losses | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments recognized in earnings	0	(5)	0	3
Other income, net of losses | Other credit derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments recognized in earnings	(7)	0	(15)	0
Other operating expenses | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments recognized in earnings	$ (2)	$ 0	$ (4)	$ 0