Derivative Instruments and Hedging Activities - Schedule of Derivative Instruments Designated as Fair Value Hedges, Gain (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Derivative Instruments, Gain (Loss) [Line Items]
Interest and fees on finance receivables and loans	$ 2,845	$ 2,721	$ 5,672	$ 5,296
Interest and dividends on investment securities and other earning assets	265	247	531	485
Interest on long-term debt	244	252	492	479
Loss on cash flow hedges to be recognized within twelve months			24
Total derivatives designated as accounting hedges | 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 (loss) gain on cash flow hedging relationships	(2)	5	(3)	10
Total derivatives designated as accounting hedges | 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 (loss) gain on cash flow hedging relationships	0	0	0	0
Total derivatives designated as accounting hedges | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Total gain on fair value hedging relationships	0	0	0	0
Total (loss) gain on cash flow hedging relationships	0	0	0	0
Total derivatives designated as accounting hedges | 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
Total derivatives designated as accounting hedges | 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
Total derivatives designated as accounting hedges | 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	0	0	0	1
Change in unrealized gain (loss) on fair value hedging instruments	0	0	0	(1)
Total derivatives designated as accounting hedges | Hedged 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
Total derivatives designated as accounting hedges | Hedged 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	(28)	(238)	(233)	(108)
Change in unrealized gain (loss) on fair value hedging instruments	28	238	233	108
Total derivatives designated as accounting hedges | Hedged 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
Total derivatives designated as accounting hedges | 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	11	(39)	(83)	166
Change in unrealized gain (loss) on fair value hedging instruments	(11)	39	83	(166)
Total derivatives designated as accounting hedges | 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
Total derivatives designated as accounting hedges | 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
Total derivatives designated as accounting hedges | Hedged variable-rate commercial loans | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge loss reclassified to earnings	(2)	5	(3)	10
Total derivatives designated as accounting hedges | Hedged 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 loss reclassified to earnings	0	0	0	0
Total derivatives designated as accounting hedges | Hedged variable-rate commercial loans | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge loss reclassified to earnings	$ 0	$ 0	$ 0	$ 0