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
	Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net, pretax	$ (5)	$ 2
Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on interest rate derivative instruments	(4)	2
Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on foreign currency derivative instruments	(1)	0
Gains on mortgage and automotive loans | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on interest rate derivative instruments	1	0
Other income | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on interest rate derivative instruments	(5)	2
Other income | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on foreign currency derivative instruments	$ (1)	$ 0