Derivative Instruments and Hedging Activities (Derivative Instruments Designated as Fair Value Hedges, Gain (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Derivative Instruments, Gain (Loss) [Line Items]
Interest and fees on finance receivables and loans	$ 2,575	$ 1,714
Interest and dividends on investment securities and other earning assets	238	188
Interest on long-term debt	227	185
Earnings on cash flow hedges to be recognized within twelve months	8
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 on cash flow hedging relationships	5	6
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 on cash flow hedging relationships	0	0
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 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 long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge	1	(2)
Change in unrealized gain (loss) on fair value hedging instruments	(1)	2
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	130	(42)
Change in unrealized gain (loss) on fair value hedging instruments	(130)	42
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	205	(304)
Change in unrealized gain (loss) on fair value hedging instruments	(205)	304
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 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 | 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	5	6
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 long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	$ 0	$ 0