Derivative Instruments and Hedging Activities (Derivative Instruments Designated as Fair Value Hedges, Gain (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Derivative Instruments, Gain (Loss) [Line Items]
Interest and fees on finance receivables and loans	$ 2,120	$ 1,619	$ 5,676	$ 4,789
Interest and dividends on investment securities and other earning assets	218	155	609	433
Interest on deposits	567	245	1,041	819
Interest on long-term debt	194	191	563	671
Earnings on cash flow hedges to be recognized within twelve months			19
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	0
Total gain (loss) on cash flow hedging relationships	5	12	16	56
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	0
Total gain (loss) on cash flow hedging relationships	0	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	0
Total gain (loss) on cash flow hedging relationships	0	0	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	0	0
Total gain (loss) on cash flow hedging relationships	(1)	0	(1)	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	0	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	1	(4)	5	69
Change in unrealized gain (loss) on fair value hedging instruments	(1)	4	(5)	(69)
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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	(97)	(34)	(186)	(51)
Change in unrealized gain (loss) on fair value hedging instruments	97	34	186	51
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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	(174)	(35)	(627)	(112)
Change in unrealized gain (loss) on fair value hedging instruments	174	35	627	112
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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	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	0
Change in unrealized gain (loss) on fair value hedging instruments	0	0	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	5	12	16	52
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	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	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	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			0	4
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
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
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
Designated as hedging instrument | Other hedge forecasted transactions | 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	0
Designated as hedging instrument | Other hedge forecasted transactions | 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	0
Designated as hedging instrument | Other hedge forecasted transactions | Interest on deposits
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	0	0	0	0
Designated as hedging instrument | Other hedge forecasted transactions | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge gain (loss) reclassified to earnings	$ (1)	$ 0	$ (1)	$ 0