Loans and Related Allowance for Credit Losses, Credit Quality Indicators for Auto Loans by Vintage (Details) - Total Consumer [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Total loans	$ 379,069		$ 379,069		$ 389,255
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Loan charge-offs, loans	1,016	$ 887	3,095	$ 2,466
Auto [Member]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Term loans by origination year, current fiscal year, finance receivable	10,123		10,123		14,069
Term loans by origination year, fiscal year before current fiscal year, finance receivable	10,298		10,298		13,414
Term loans by origination year, two years before current fiscal year, finance receivable	9,797		9,797		12,970
Term loans by origination year, three years before current fiscal year, finance receivable	8,824		8,824		4,544
Term loans by origination year, four years before current fiscal year, finance receivable	2,681		2,681		2,274
Term loans by origination year, more than five years before current fiscal year, finance receivable	1,092		1,092		491
Total loans	42,815		42,815		47,762
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Term loans by origination year, current fiscal year, charge-offs			4		15
Term loans by origination year, fiscal year before current fiscal year, charge-offs			35		265
Term loans by origination year, two years before current fiscal year, charge-offs			190		392
Term loans by origination year, three years before current fiscal year, charge-offs			213		99
Term loans by origination year, four years before current fiscal year, charge-offs			44		52
Term loans by origination year, more than five years before current fiscal year, charge-offs			19		9
Loan charge-offs, loans	158	$ 223	505	$ 623	832
Auto [Member] | FICO 740 or more [Member]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Term loans by origination year, current fiscal year, finance receivable	6,457		6,457		9,460
Term loans by origination year, fiscal year before current fiscal year, finance receivable	6,905		6,905		6,637
Term loans by origination year, two years before current fiscal year, finance receivable	4,885		4,885		5,487
Term loans by origination year, three years before current fiscal year, finance receivable	3,721		3,721		1,853
Term loans by origination year, four years before current fiscal year, finance receivable	1,057		1,057		963
Term loans by origination year, more than five years before current fiscal year, finance receivable	393		393		176
Total loans	23,418		23,418		24,576
Auto [Member] | FICO 700 to 739 [Member]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Term loans by origination year, current fiscal year, finance receivable	1,877		1,877		2,232
Term loans by origination year, fiscal year before current fiscal year, finance receivable	1,496		1,496		1,969
Term loans by origination year, two years before current fiscal year, finance receivable	1,375		1,375		1,861
Term loans by origination year, three years before current fiscal year, finance receivable	1,205		1,205		701
Term loans by origination year, four years before current fiscal year, finance receivable	390		390		347
Term loans by origination year, more than five years before current fiscal year, finance receivable	153		153		68
Total loans	6,496		6,496		7,178
Auto [Member] | FICO 660 to 699 [Member]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Term loans by origination year, current fiscal year, finance receivable	1,211		1,211		1,405
Term loans by origination year, fiscal year before current fiscal year, finance receivable	986		986		1,745
Term loans by origination year, two years before current fiscal year, finance receivable	1,171		1,171		1,729
Term loans by origination year, three years before current fiscal year, finance receivable	1,096		1,096		623
Term loans by origination year, four years before current fiscal year, finance receivable	349		349		295
Term loans by origination year, more than five years before current fiscal year, finance receivable	140		140		61
Total loans	4,953		4,953		5,858
Auto [Member] | FICO 620 to 659 [Member]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Term loans by origination year, current fiscal year, finance receivable	395		395		572
Term loans by origination year, fiscal year before current fiscal year, finance receivable	450		450		1,162
Term loans by origination year, two years before current fiscal year, finance receivable	775		775		1,228
Term loans by origination year, three years before current fiscal year, finance receivable	781		781		425
Term loans by origination year, four years before current fiscal year, finance receivable	244		244		195
Term loans by origination year, more than five years before current fiscal year, finance receivable	101		101		46
Total loans	2,746		2,746		3,628
Auto [Member] | FICO less than 620 [Member]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Term loans by origination year, current fiscal year, finance receivable	179		179		388
Term loans by origination year, fiscal year before current fiscal year, finance receivable	456		456		1,876
Term loans by origination year, two years before current fiscal year, finance receivable	1,567		1,567		2,621
Term loans by origination year, three years before current fiscal year, finance receivable	1,984		1,984		915
Term loans by origination year, four years before current fiscal year, finance receivable	622		622		452
Term loans by origination year, more than five years before current fiscal year, finance receivable	294		294		130
Total loans	5,102		5,102		6,382
Auto [Member] | No FICO available [Member]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Term loans by origination year, current fiscal year, finance receivable	4		4		12
Term loans by origination year, fiscal year before current fiscal year, finance receivable	5		5		25
Term loans by origination year, two years before current fiscal year, finance receivable	24		24		44
Term loans by origination year, three years before current fiscal year, finance receivable	37		37		27
Term loans by origination year, four years before current fiscal year, finance receivable	19		19		22
Term loans by origination year, more than five years before current fiscal year, finance receivable	11		11		10
Total loans	100		100		140
Auto [Member] | Current-29 days past due [Member]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Term loans by origination year, current fiscal year, finance receivable	10,104		10,104		14,022
Term loans by origination year, fiscal year before current fiscal year, finance receivable	10,233		10,233		13,052
Term loans by origination year, two years before current fiscal year, finance receivable	9,491		9,491		12,376
Term loans by origination year, three years before current fiscal year, finance receivable	8,389		8,389		4,335
Term loans by origination year, four years before current fiscal year, finance receivable	2,543		2,543		2,161
Term loans by origination year, more than five years before current fiscal year, finance receivable	1,018		1,018		448
Total loans	41,778		41,778		46,394
Auto [Member] | 30 to 89 days past due [Member]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Term loans by origination year, current fiscal year, finance receivable	18		18		43
Term loans by origination year, fiscal year before current fiscal year, finance receivable	60		60		328
Term loans by origination year, two years before current fiscal year, finance receivable	279		279		545
Term loans by origination year, three years before current fiscal year, finance receivable	402		402		195
Term loans by origination year, four years before current fiscal year, finance receivable	129		129		106
Term loans by origination year, more than five years before current fiscal year, finance receivable	69		69		40
Total loans	957		957		1,257
Auto [Member] | 90 days or more past due [Member]
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Term loans by origination year, current fiscal year, finance receivable	1		1		4
Term loans by origination year, fiscal year before current fiscal year, finance receivable	5		5		34
Term loans by origination year, two years before current fiscal year, finance receivable	27		27		49
Term loans by origination year, three years before current fiscal year, finance receivable	33		33		14
Term loans by origination year, four years before current fiscal year, finance receivable	9		9		7
Term loans by origination year, more than five years before current fiscal year, finance receivable	5		5		3
Total loans	$ 80		$ 80		$ 111