Derivative Instruments and Hedging Activities (Statement of Gains and Losses on Derivative Instruments Reported in Statement of Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest and fees on finance receivables and loans	$ 1,859	$ 1,708	$ 5,526	$ 4,898
Interest and dividends on investment securities and other earning assets	237	198	721	562
Interest on deposits	658	462	1,901	1,212
Interest on long-term debt	378	451	1,204	1,296
Earnings on cash flow hedges to be recognized within twelve months			5
Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net, pretax	1	(1)	(8)	5
Interest rate contracts \| Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net, pretax	0	0	(6)	0
Foreign exchange contracts \| Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net, pretax	1	(1)	(2)	5
Gains on mortgage and automotive loans \| Interest rate contracts \| Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net, pretax	0	0	1	0
Other income \| Interest rate contracts \| Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net, pretax	0	0	(7)	0
Other income \| Foreign exchange contracts \| Not designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments, net, pretax	1	(1)	(2)	5
Deposit liabilities \| Interest and fees on finance receivables and loans \| Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0	0	0
Deposit liabilities \| Interest and dividends on investment securities and other earning assets \| Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0	0	0
Deposit liabilities \| Interest on deposits \| Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	(2)	0	(1)	0
Deposit liabilities \| Interest on long-term debt \| Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0	0	0
Variable-rate borrowings \| Interest and fees on finance receivables and loans \| Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0	0	0
Variable-rate borrowings \| Interest and dividends on investment securities and other earning assets \| Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0	0	0
Variable-rate borrowings \| Interest on deposits \| Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0	0	0
Variable-rate borrowings \| Interest on long-term debt \| Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	$ 4	$ 0	$ 12	$ 0

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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Interest and fee income generated by loans the Entity intends and has the ability to hold for the foreseeable future, or until maturity or payoff, including commercial and consumer loans, whether domestic or foreign, which may consist of: (1) industrial and agricultural; (2) real estate; and (3) real estate construction loans; (4) trade financing; (5) lease financing; (6) home equity lines-of-credit; (7) automobile and other vehicle loans; and (8) credit card and other revolving-type loans. Also includes interest income for leases held by the Entity.

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