Derivative Instruments and Hedging Activities - Schedule of Derivative Instruments Designated as Fair Value Hedges, Gain (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Derivative Instruments, Gain (Loss) [Line Items]
Interest and fees on finance receivables and loans	$ 2,709	$ 2,827
Interest and dividends on investment securities and other earning assets	230	266
Interest on long-term debt	271	248
Loss on cash flow hedges to be recognized within twelve months	31
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
Total loss on cash flow hedging relationships	(7)	(1)
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
Total loss on cash flow hedging relationships	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
Total loss on cash flow hedging relationships	0	0
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
Change in unrealized gain (loss) on fair value hedging instruments	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	130	(205)
Change in unrealized gain (loss) on fair value hedging instruments	(130)	205
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
Change in unrealized gain (loss) on fair value hedging instruments	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	29	(94)
Change in unrealized gain (loss) on fair value hedging instruments	(29)	94
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
Change in unrealized gain (loss) on fair value hedging instruments	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
Change in unrealized gain (loss) on fair value hedging instruments	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	(7)	(1)
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
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