Derivative Instruments and Hedging Activities (Derivative Instruments Designated as Fair Value Hedges, Gain (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Derivative Instruments, Gain (Loss) [Line Items]
Interest and fees on finance receivables and loans	$ 1,714	$ 1,582
Interest and dividends on investment securities and other earning assets	188	131
Interest on deposits	211	306
Interest on long-term debt	185	250
Earnings on cash flow hedges to be recognized within twelve months	20
Designated as hedging instrument | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Total gain on fair value hedging relationships	0	0
Total gain (loss) on cash flow hedging relationships	6	22
Designated as hedging instrument | Interest and dividends on investment securities and other earning assets
Derivative Instruments, Gain (Loss) [Line Items]
Total gain on fair value hedging relationships	0	0
Total gain (loss) on cash flow hedging relationships	0	0
Designated as hedging instrument | Interest on deposits
Derivative Instruments, Gain (Loss) [Line Items]
Total gain on fair value hedging relationships	0	0
Total gain (loss) on cash flow hedging relationships	0	(1)
Designated as hedging instrument | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Total gain on fair value hedging relationships	0	0
Total gain (loss) on cash flow hedging relationships	0	0
Designated as hedging instrument | Unsecured debt | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge	0	0
Change in unrealized gain (loss) on fair value hedging instruments	0	0
Designated as hedging instrument | Unsecured debt | Interest and dividends on investment securities and other earning assets
Derivative Instruments, Gain (Loss) [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge	0	0
Change in unrealized gain (loss) on fair value hedging instruments	0	0
Designated as hedging instrument | Unsecured debt | Interest on deposits
Derivative Instruments, Gain (Loss) [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge	0	0
Change in unrealized gain (loss) on fair value hedging instruments	0	0
Designated as hedging instrument | Unsecured debt | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge	(2)	139
Change in unrealized gain (loss) on fair value hedging instruments	2	(139)
Designated as hedging instrument | Available-for-sale securities | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge	0	0
Change in unrealized gain (loss) on fair value hedging instruments	0	0
Designated as hedging instrument | Available-for-sale securities | Interest and dividends on investment securities and other earning assets
Derivative Instruments, Gain (Loss) [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge	(42)	(13)
Change in unrealized gain (loss) on fair value hedging instruments	42	13
Designated as hedging instrument | Available-for-sale securities | Interest on deposits
Derivative Instruments, Gain (Loss) [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge	0	0
Change in unrealized gain (loss) on fair value hedging instruments	0	0
Designated as hedging instrument | Available-for-sale securities | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge	0	0
Change in unrealized gain (loss) on fair value hedging instruments	0	0
Designated as hedging instrument | Fixed-rate automotive loans | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge	(304)	(39)
Change in unrealized gain (loss) on fair value hedging instruments	304	39
Designated as hedging instrument | Fixed-rate automotive loans | Interest and dividends on investment securities and other earning assets
Derivative Instruments, Gain (Loss) [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge	0	0
Change in unrealized gain (loss) on fair value hedging instruments	0	0
Designated as hedging instrument | Fixed-rate automotive loans | Interest on deposits
Derivative Instruments, Gain (Loss) [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge	0	0
Change in unrealized gain (loss) on fair value hedging instruments	0	0
Designated as hedging instrument | Fixed-rate automotive loans | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge	0	0
Change in unrealized gain (loss) on fair value hedging instruments	0	0
Designated as hedging instrument | Deposit liabilities | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0
Designated as hedging instrument | Deposit liabilities | Interest and dividends on investment securities and other earning assets
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0
Designated as hedging instrument | Deposit liabilities | Interest on deposits
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	(1)
Designated as hedging instrument | Deposit liabilities | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0
Designated as hedging instrument | Variable-rate commercial loans | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	6	22
Designated as hedging instrument | Variable-rate commercial loans | Interest and dividends on investment securities and other earning assets
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0
Designated as hedging instrument | Variable-rate commercial loans | Interest on deposits
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0
Designated as hedging instrument | Variable-rate commercial loans | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	$ 0	$ 0