Loans and Related Allowance for Credit Losses (Credit Quality Indicators for Automobile, Credit Card, Education and Other Consumer Loan Classes) (Details) - 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, net	[1]	$ 321,381		$ 321,381		$ 321,508
Gross charge-offs
Total		376	$ 233	1,081	$ 808
Updated FICO scores
Gross charge-offs
Year one				4		8
Year two				33		24
Year three				21		22
Year four				13		17
Year five				9		30
Prior				18		20
Total				98		121
Updated FICO scores | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		4,988		4,988		5,797
Year two		4,320		4,320		3,630
Year three		2,629		2,629		2,912
Year four		1,958		1,958		1,174
Year five		673		673		1,004
Prior		567		567		343
Total loans, net		15,135		15,135		14,860
Updated FICO scores | Greater than or equal to 780 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		2,590		2,590		2,722
Year two		1,901		1,901		1,650
Year three		1,227		1,227		1,483
Year four		1,010		1,010		535
Year five		304		304		368
Prior		181		181		88
Total loans, net		7,213		7,213		6,846
Updated FICO scores | 720 to 779 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		1,533		1,533		1,797
Year two		1,309		1,309		1,104
Year three		747		747		778
Year four		494		494		301
Year five		164		164		250
Prior		132		132		80
Total loans, net		4,379		4,379		4,310
Updated FICO scores | 660 to 719 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		720		720		1,014
Year two		756		756		604
Year three		417		417		408
Year four		266		266		186
Year five		104		104		186
Prior		106		106		70
Total loans, net		2,369		2,369		2,468
Updated FICO scores | Less than 660 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		145		145		264
Year two		354		354		272
Year three		238		238		243
Year four		188		188		152
Year five		101		101		200
Prior		148		148		105
Total loans, net		1,174		1,174		1,236
Credit card
Gross charge-offs
Revolving Loans				240		290
Revolving Loans Converted to Term				28		29
Total				268		319
Credit card | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Revolving Loans		6,748		6,748		7,111
Revolving Loans Converted to Term		79		79		69
Total loans, net		6,827		6,827		7,180
Credit card | Greater than or equal to 780 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Revolving Loans		2,000		2,000		2,017
Revolving Loans Converted to Term		1		1		1
Total loans, net		2,001		2,001		2,018
Credit card | 720 to 779 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Revolving Loans		1,864		1,864		1,976
Revolving Loans Converted to Term		5		5		4
Total loans, net		1,869		1,869		1,980
Credit card | 660 to 719 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Revolving Loans		1,836		1,836		1,979
Revolving Loans Converted to Term		15		15		13
Total loans, net		1,851		1,851		1,992
Credit card | Less than 660 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Revolving Loans		946		946		1,036
Revolving Loans Converted to Term		55		55		48
Total loans, net		1,001		1,001		1,084
Credit card | No FICO score available or required | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Revolving Loans		102		102		103
Revolving Loans Converted to Term		3		3		3
Total loans, net		105		105		106
Education
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		49		49		106
Year two		124		124		160
Year three		146		146		83
Year four		72		72		68
Year five		56		56		85
Prior		1,246		1,246		1,443
Total loans, net		1,693		1,693		1,945
Gross charge-offs
Year three				1		1
Year four				1		1
Year five				1		2
Prior				10		13
Total				13		17
Education | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		49		49		106
Year two		124		124		160
Year three		146		146		83
Year four		72		72		68
Year five		56		56		85
Prior		528		528		538
Total loans, net		975		975		1,040
Education | Greater than or equal to 780 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		10		10		35
Year two		61		61		88
Year three		83		83		45
Year four		41		41		40
Year five		34		34		51
Prior		332		332		331
Total loans, net		561		561		590
Education | 720 to 779 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		14		14		32
Year two		39		39		47
Year three		40		40		24
Year four		21		21		19
Year five		15		15		24
Prior		123		123		131
Total loans, net		252		252		277
Education | 660 to 719 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		10		10		20
Year two		15		15		17
Year three		15		15		8
Year four		6		6		6
Year five		5		5		8
Prior		51		51		54
Total loans, net		102		102		113
Education | Less than 660 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		2		2		4
Year two		3		3		3
Year three		4		4		2
Year four		1		1		1
Year five		1		1		2
Prior		21		21		21
Total loans, net		32		32		33
Education | No FICO score available or required | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		13		13		15
Year two		6		6		5
Year three		4		4		4
Year four		3		3		2
Year five		1		1
Prior		1		1		1
Total loans, net		28		28		27
Education | Other internal credit metrics
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Prior		718		718		905
Total loans, net		718		718		905
Other consumer
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		599		599		712
Year two		476		476		573
Year three		383		383		222
Year four		113		113		139
Year five		49		49		137
Prior		125		125		75
Revolving Loans		2,303		2,303		2,398
Revolving Loans Converted to Term		15		15		15
Total loans, net		4,063		4,063		4,271
Gross charge-offs
Year one				55		75
Year two				19		23
Year three				19		18
Year four				11		14
Year five				6		14
Prior				8		8
Revolving Loans				8		11
Revolving Loans Converted to Term				1		1
Total				127		164
Other consumer | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		593		593		693
Year two		466		466		476
Year three		290		290		189
Year four		99		99		91
Year five		37		37		66
Prior		33		33		41
Revolving Loans		232		232		249
Revolving Loans Converted to Term		4		4		5
Total loans, net		1,754		1,754		1,810
Other consumer | Greater than or equal to 780 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		189		189		241
Year two		157		157		127
Year three		75		75		47
Year four		24		24		21
Year five		8		8		14
Prior		8		8		11
Revolving Loans		37		37		39
Revolving Loans Converted to Term		1		1		1
Total loans, net		499		499		501
Other consumer | 720 to 779 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		232		232		286
Year two		171		171		157
Year three		89		89		54
Year four		28		28		26
Year five		10		10		17
Prior		9		9		11
Revolving Loans		74		74		80
Revolving Loans Converted to Term		1		1		1
Total loans, net		614		614		632
Other consumer | 660 to 719 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		163		163		147
Year two		105		105		140
Year three		87		87		57
Year four		29		29		27
Year five		11		11		21
Prior		9		9		11
Revolving Loans		80		80		87
Revolving Loans Converted to Term		1		1		2
Total loans, net		485		485		492
Other consumer | Less than 660 | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		9		9		19
Year two		33		33		52
Year three		39		39		31
Year four		18		18		17
Year five		8		8		14
Prior		7		7		8
Revolving Loans		41		41		43
Revolving Loans Converted to Term		1		1		1
Total loans, net		156		156		185
Other consumer | Other internal credit metrics
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		6		6		19
Year two		10		10		97
Year three		93		93		33
Year four		14		14		48
Year five		12		12		71
Prior		92		92		34
Revolving Loans		2,071		2,071		2,149
Revolving Loans Converted to Term		11		11		10
Total loans, net		$ 2,309		$ 2,309		$ 2,461

[1] Our consolidated assets included the following for which we have elected the fair value option: Loans held for sale of $0.7 billion, Loans held for investment of $1.2 billion and Other assets of $0.1 billion at September 30, 2024. Comparable amounts at December 31, 2023 were $0.7 billion, $1.2 billion and $0.1 billion, respectively.