Derivative Instruments and Hedging Activities (Derivative Instruments Designated as Fair Value Hedges, Gain (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Interest and fees on finance receivables and loans			$ 8,099	$ 6,468	$ 6,581
Interest and dividends on investment securities and other earning assets			841	600	736
Interest on deposits			1,987	1,045	1,952
Interest on long-term debt			763	860	1,249
Earnings on cash flow hedges to be recognized within twelve months			14
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			21	62	73
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			0	(1)	(8)
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			(1)	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	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			1	68	(135)
Change in unrealized gain (loss) on fair value hedging instruments			(1)	(68)	135
Designated as hedging instrument | Fixed-rate FHLB Advances | 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 | Fixed-rate FHLB Advances | 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 FHLB Advances | 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 FHLB Advances | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge			(5)	0	0
Change in unrealized gain (loss) on fair value hedging instruments			5	0	0
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			(185)	(40)	38
Change in unrealized gain (loss) on fair value hedging instruments			185	40	(38)
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			(599)	(215)	139
Change in unrealized gain (loss) on fair value hedging instruments			599	215	(139)
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 | 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			0	(1)	(8)
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			21	58	73
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			0	4	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
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
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
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
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			$ 0