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		12 Months Ended
		Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Total loans, net	[1]	$ 319,781		$ 321,508
Gross charge-offs
Total		330	$ 282
Updated FICO scores
Gross charge-offs
Year one				8
Year two		11		24
Year three		6		22
Year four		5		17
Year five		3		30
Prior		7		20
Total		32		121
Updated FICO scores | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		1,582		5,797
Year two		5,318		3,630
Year three		3,283		2,912
Year four		2,578		1,174
Year five		991		1,004
Prior		1,036		343
Total loans, net		14,788		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		927		2,722
Year two		2,230		1,650
Year three		1,480		1,483
Year four		1,288		535
Year five		443		368
Prior		340		88
Total loans, net		6,708		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		438		1,797
Year two		1,727		1,104
Year three		983		778
Year four		689		301
Year five		250		250
Prior		252		80
Total loans, net		4,339		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		206		1,014
Year two		1,009		604
Year three		549		408
Year four		368		186
Year five		159		186
Prior		195		70
Total loans, net		2,486		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		11		264
Year two		352		272
Year three		271		243
Year four		233		152
Year five		139		200
Prior		249		105
Total loans, net		1,255		1,236
Credit card
Gross charge-offs
Revolving Loans		83		290
Revolving Loans Converted to Term		9		29
Total		92		319
Credit card | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Revolving Loans		6,814		7,111
Revolving Loans Converted to Term		73		69
Total loans, net		6,887		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		1,938		2,017
Revolving Loans Converted to Term		1		1
Total loans, net		1,939		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		1,879		1,976
Revolving Loans Converted to Term		4		4
Total loans, net		1,883		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		1,901		1,979
Revolving Loans Converted to Term		14		13
Total loans, net		1,915		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		989		1,036
Revolving Loans Converted to Term		51		48
Total loans, net		1,040		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		107		103
Revolving Loans Converted to Term		3		3
Total loans, net		110		106
Education
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		13		106
Year two		133		160
Year three		155		83
Year four		78		68
Year five		64		85
Prior		1,416		1,443
Total loans, net		1,859		1,945
Gross charge-offs
Year three				1
Year four				1
Year five				2
Prior		4		13
Total		4		17
Education | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		13		106
Year two		133		160
Year three		155		83
Year four		78		68
Year five		64		85
Prior		590		538
Total loans, net		1,033		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		1		35
Year two		61		88
Year three		85		45
Year four		44		40
Year five		37		51
Prior		360		331
Total loans, net		588		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		4		32
Year two		44		47
Year three		45		24
Year four		23		19
Year five		18		24
Prior		146		131
Total loans, net		280		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		4		20
Year two		17		17
Year three		17		8
Year four		7		6
Year five		6		8
Prior		60		54
Total loans, net		111		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		1		4
Year two		3		3
Year three		3		2
Year four		1		1
Year five		1		2
Prior		23		21
Total loans, net		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		3		15
Year two		8		5
Year three		5		4
Year four		3		2
Year five		2
Prior		1		1
Total loans, net		22		27
Education | Other internal credit metrics
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Prior		826		905
Total loans, net		826		905
Other consumer
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		173		712
Year two		626		573
Year three		511		222
Year four		183		139
Year five		82		137
Prior		174		75
Revolving Loans		2,355		2,398
Revolving Loans Converted to Term		16		15
Total loans, net		4,120		4,271
Gross charge-offs
Year one		17		75
Year two		6		23
Year three		6		18
Year four		5		14
Year five		2		14
Prior		4		8
Revolving Loans		3		11
Revolving Loans Converted to Term				1
Total		43		164
Other consumer | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		170		693
Year two		615		476
Year three		410		189
Year four		153		91
Year five		69		66
Prior		73		41
Revolving Loans		236		249
Revolving Loans Converted to Term		5		5
Total loans, net		1,731		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		49		241
Year two		219		127
Year three		104		47
Year four		37		21
Year five		15		14
Prior		17		11
Revolving Loans		36		39
Revolving Loans Converted to Term		1		1
Total loans, net		478		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		77		286
Year two		242		157
Year three		130		54
Year four		43		26
Year five		19		17
Prior		19		11
Revolving Loans		75		80
Revolving Loans Converted to Term		1		1
Total loans, net		606		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		44		147
Year two		126		140
Year three		125		57
Year four		46		27
Year five		21		21
Prior		21		11
Revolving Loans		83		87
Revolving Loans Converted to Term		2		2
Total loans, net		468		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				19
Year two		28		52
Year three		51		31
Year four		27		17
Year five		14		14
Prior		16		8
Revolving Loans		42		43
Revolving Loans Converted to Term		1		1
Total loans, net		179		185
Other consumer | Other internal credit metrics
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		3		19
Year two		11		97
Year three		101		33
Year four		30		48
Year five		13		71
Prior		101		34
Revolving Loans		2,119		2,149
Revolving Loans Converted to Term		11		10
Total loans, net		$ 2,389		$ 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 March 31, 2024. Comparable amounts at December 31, 2023 were $0.7 billion, $1.2 billion and $0.1 billion, respectively.