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, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Derivative Instruments, Gain (Loss) [Line Items]
Interest and fees on finance receivables and loans	$ 2,624	$ 2,845	$ 5,333	$ 5,672
Interest and dividends on investment securities and other earning assets	248	265	478	531
Interest on long-term debt	258	244	529	492
Loss on cash flow hedges to be recognized within twelve months			27
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 on cash flow hedging relationships	(8)	(2)	(15)	(3)
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 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 on cash flow hedging relationships	0	0	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	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	84	(28)	214	(233)
Change in unrealized gain (loss) on fair value hedging instruments	(84)	28	(214)	233
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	12	11	41	(83)
Change in unrealized gain (loss) on fair value hedging instruments	(12)	(11)	(41)	83
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	(8)	(2)	(15)	(3)
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