Derivative Instruments and Hedging Activities (Derivative Instruments Designated as Fair Value Hedges, Gain (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Interest and fees on finance receivables and loans	$ 6,468	$ 6,581	$ 7,337
Interest and dividends on investment securities and other earning assets	600	736	955
Interest on deposits	1,045	1,952	2,538
Interest on long-term debt	860	1,249	1,570
Earnings on cash flow hedges to be recognized within twelve months	21
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	0
Total gain (loss) on cash flow hedging relationships	62	73	0
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	0
Total gain (loss) on cash flow hedging relationships	0	0	0
Designated as hedging instrument | Interest on deposits
Derivative Instruments, Gain (Loss) [Line Items]
Total gain on fair value hedging relationships	0	0	0
Total gain (loss) on cash flow hedging relationships	(1)	(8)	(4)
Designated as hedging instrument | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Total gain on fair value hedging relationships	0	0	0
Total gain (loss) on cash flow hedging relationships	0	0	15
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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	68	(135)	41
Change in unrealized gain (loss) on fair value hedging instruments	(68)	135	(41)
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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	(40)	38	28
Change in unrealized gain (loss) on fair value hedging instruments	40	(38)	(28)
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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	(215)	139	138
Change in unrealized gain (loss) on fair value hedging instruments	215	(139)	(138)
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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	0	0
Designated as hedging instrument | Variable-rate borrowings | 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	0
Designated as hedging instrument | Variable-rate borrowings | 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	0
Designated as hedging instrument | Variable-rate borrowings | Interest on deposits
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0	0
Designated as hedging instrument | Variable-rate borrowings | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0	15
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	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	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	(1)	(8)	(4)
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	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	58	73	0
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	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	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	0
Designated as hedging instrument | Variable-rate commercial borrowings probable not to occur | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	4	0	0
Designated as hedging instrument | Variable-rate commercial borrowings probable not to occur | 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	0
Designated as hedging instrument | Variable-rate commercial borrowings probable not to occur | Interest on deposits
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0	0
Designated as hedging instrument | Variable-rate commercial borrowings probable not to occur | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	$ 0	$ 0	$ 0