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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net, pretax	$ (4)	$ 4	$ (9)	$ 6
Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net, pretax	(2)	(2)	(6)	0
Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net, pretax	(2)	6	(3)	6
Gains on mortgage and automotive loans | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net, pretax	0	0	1	0
Other income | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net, pretax	(2)	(2)	(7)	0
Other income | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net, pretax	$ (2)	$ 6	$ (3)	$ 6