Derivative Instruments and Hedging Activities (Derivative Instruments Designated as Fair Value Hedges, Gain (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Derivative Instruments, Gain (Loss) [Line Items]
Interest and fees on finance receivables and loans	$ 11,020	$ 8,099	$ 6,468
Interest and dividends on investment securities and other earning assets	1,022	841	600
Interest on deposits	5,819	1,987	1,045
Interest on long-term debt	1,001	763	860
Loss on cash flow hedges to be recognized within twelve months	12
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
Total gain (loss) on cash flow hedging relationships	14	21	62
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
Total gain (loss) on cash flow hedging relationships	0	0	0
Total derivatives designated as accounting hedges | 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	0	(1)
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
Total gain (loss) on cash flow hedging relationships	0	(1)	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
Change in unrealized gain (loss) on fair value hedging instruments	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
Change in unrealized gain (loss) on fair value hedging instruments	0	0	0
Total derivatives designated as accounting hedges | 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
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	1	1	68
Change in unrealized gain (loss) on fair value hedging instruments	(1)	(1)	(68)
Total derivatives designated as accounting hedges | Hedged 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
Total derivatives designated as accounting hedges | Hedged 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
Total derivatives designated as accounting hedges | Hedged 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
Total derivatives designated as accounting hedges | Hedged 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	0	(5)	0
Change in unrealized gain (loss) on fair value hedging instruments	0	5	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
Change in unrealized gain (loss) on fair value hedging instruments	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	76	(185)	(40)
Change in unrealized gain (loss) on fair value hedging instruments	(76)	185	40
Total derivatives designated as accounting hedges | Hedged 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
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
Change in unrealized gain (loss) on fair value hedging instruments	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	491	(599)	(215)
Change in unrealized gain (loss) on fair value hedging instruments	(491)	599	215
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
Change in unrealized gain (loss) on fair value hedging instruments	0	0	0
Total derivatives designated as accounting hedges | 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
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
Change in unrealized gain (loss) on fair value hedging instruments	0	0	0
Total derivatives designated as accounting hedges | Hedged variable rate borrowings | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge loss reclassified to earnings	0	0	0
Total derivatives designated as accounting hedges | Hedged variable rate borrowings | 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
Total derivatives designated as accounting hedges | Hedged variable rate borrowings | Interest on deposits
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge loss reclassified to earnings	0	0	(1)
Total derivatives designated as accounting hedges | Hedged variable rate borrowings | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge loss reclassified to earnings	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	14	21	58
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
Total derivatives designated as accounting hedges | Hedged variable-rate commercial loans | Interest on deposits
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge loss reclassified to earnings	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
Total derivatives designated as accounting hedges | Reclassified from accumulated other comprehensive loss into income as a result of a forecasted transaction being probable not to occur | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge loss reclassified to earnings	0	0	4
Total derivatives designated as accounting hedges | Reclassified from accumulated other comprehensive loss into income as a result of a forecasted transaction being 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 loss reclassified to earnings	0	0	0
Total derivatives designated as accounting hedges | Reclassified from accumulated other comprehensive loss into income as a result of a forecasted transaction being probable not to occur | Interest on deposits
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge loss reclassified to earnings	0	0	0
Total derivatives designated as accounting hedges | Reclassified from accumulated other comprehensive loss into income as a result of a forecasted transaction being probable not to occur | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge loss reclassified to earnings	0	0	0
Total derivatives designated as accounting hedges | Other hedged forecasted transactions | Interest and fees on finance receivables and loans
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge loss reclassified to earnings	0	0	0
Total derivatives designated as accounting hedges | Other hedged forecasted transactions | 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
Total derivatives designated as accounting hedges | Other hedged forecasted transactions | Interest on deposits
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge loss reclassified to earnings	0	0	0
Total derivatives designated as accounting hedges | Other hedged forecasted transactions | Interest on long-term debt
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate cash flow hedge loss reclassified to earnings	$ 0	$ (1)	$ 0