Derivative Instruments and Hedging Activities (Interest and Amortization on Derivative Instruments) (Details) - Total derivatives designated as accounting hedges - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) on fair value hedging relationships	$ 648	$ 147	$ (168)
Interest and dividends on investment securities and other earning assets
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) on fair value hedging relationships	157	16	(10)
Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) on fair value hedging relationships	11	3	(4)
Unsecured debt | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on amortization of deferred basis adjustments	0	0	0
Gain (loss) on interest for qualifying hedge	0	0	0
Unsecured debt | Interest and dividends on investment securities and other earning assets
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on amortization of deferred basis adjustments	0	0	0
Gain (loss) on interest for qualifying hedge	0	0	0
Unsecured debt | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on amortization of deferred basis adjustments	9	5	4
Gain (loss) on interest for qualifying hedge	0	1	5
Federal Home Loan Bank certificates and obligations | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on amortization of deferred basis adjustments	0	0	0
Federal Home Loan Bank certificates and obligations | Interest and dividends on investment securities and other earning assets
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on amortization of deferred basis adjustments	0	0	0
Federal Home Loan Bank certificates and obligations | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on amortization of deferred basis adjustments	2	(3)	(13)
Hedged available-for-sale securities | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on amortization of deferred basis adjustments	0	0	0
Gain (loss) on interest for qualifying hedge	0	0	0
Hedged available-for-sale securities | Interest and dividends on investment securities and other earning assets
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on amortization of deferred basis adjustments	23	17	(4)
Gain (loss) on interest for qualifying hedge	134	(1)	(6)
Hedged available-for-sale securities | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on amortization of deferred basis adjustments	0	0	0
Gain (loss) on interest for qualifying hedge	0	0	0
Fixed-rate automotive loans | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on amortization of deferred basis adjustments	32	18	(46)
Gain (loss) on interest for qualifying hedge	616	129	(122)
Fixed-rate automotive loans | Interest and dividends on investment securities and other earning assets
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on amortization of deferred basis adjustments	0	0	0
Gain (loss) on interest for qualifying hedge	0	0	0
Fixed-rate automotive loans | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on amortization of deferred basis adjustments	0	0	0
Gain (loss) on interest for qualifying hedge	$ 0	$ 0	$ 0