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		6 Months Ended		12 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Total loans, net	[1]	$ 321,429		$ 321,429		$ 321,508
Gross charge-offs
Total		375	$ 293	705	$ 575
Updated FICO scores
Gross charge-offs
Year one						8
Year two				23		24
Year three				13		22
Year four				9		17
Year five				6		30
Prior				13		20
Total				64		121
Updated FICO scores | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		3,199		3,199		5,797
Year two		4,794		4,794		3,630
Year three		2,954		2,954		2,912
Year four		2,265		2,265		1,174
Year five		827		827		1,004
Prior		781		781		343
Total loans, net		14,820		14,820		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		1,663		1,663		2,722
Year two		2,086		2,086		1,650
Year three		1,387		1,387		1,483
Year four		1,171		1,171		535
Year five		377		377		368
Prior		259		259		88
Total loans, net		6,943		6,943		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		1,000		1,000		1,797
Year two		1,496		1,496		1,104
Year three		842		842		778
Year four		578		578		301
Year five		202		202		250
Prior		184		184		80
Total loans, net		4,302		4,302		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		469		469		1,014
Year two		860		860		604
Year three		473		473		408
Year four		307		307		186
Year five		129		129		186
Prior		144		144		70
Total loans, net		2,382		2,382		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		67		67		264
Year two		352		352		272
Year three		252		252		243
Year four		209		209		152
Year five		119		119		200
Prior		194		194		105
Total loans, net		1,193		1,193		1,236
Credit card
Gross charge-offs
Revolving Loans				164		290
Revolving Loans Converted to Term				18		29
Total				182		319
Credit card | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Revolving Loans		6,774		6,774		7,111
Revolving Loans Converted to Term		75		75		69
Total loans, net		6,849		6,849		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		1,975		1,975		2,017
Revolving Loans Converted to Term		1		1		1
Total loans, net		1,976		1,976		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		1,885		1,885		1,976
Revolving Loans Converted to Term		4		4		4
Total loans, net		1,889		1,889		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		1,857		1,857		1,979
Revolving Loans Converted to Term		14		14		13
Total loans, net		1,871		1,871		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		952		952		1,036
Revolving Loans Converted to Term		53		53		48
Total loans, net		1,005		1,005		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		105		105		103
Revolving Loans Converted to Term		3		3		3
Total loans, net		108		108		106
Education
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		22		22		106
Year two		129		129		160
Year three		150		150		83
Year four		75		75		68
Year five		60		60		85
Prior		1,296		1,296		1,443
Total loans, net		1,732		1,732		1,945
Gross charge-offs
Year three				1		1
Year four						1
Year five				1		2
Prior				7		13
Total				9		17
Education | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		22		22		106
Year two		129		129		160
Year three		150		150		83
Year four		75		75		68
Year five		60		60		85
Prior		556		556		538
Total loans, net		992		992		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		7		7		35
Year two		65		65		88
Year three		87		87		45
Year four		42		42		40
Year five		37		37		51
Prior		347		347		331
Total loans, net		585		585		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		7		7		32
Year two		41		41		47
Year three		41		41		24
Year four		22		22		19
Year five		16		16		24
Prior		131		131		131
Total loans, net		258		258		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		4		20
Year two		14		14		17
Year three		15		15		8
Year four		7		7		6
Year five		5		5		8
Prior		55		55		54
Total loans, net		100		100		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		1		4
Year two		3		3		3
Year three		3		3		2
Year four		1		1		1
Year five		1		1		2
Prior		22		22		21
Total loans, net		31		31		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		3		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		18		18		27
Education | Other internal credit metrics
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Prior		740		740		905
Total loans, net		740		740		905
Other consumer
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		389		389		712
Year two		549		549		573
Year three		443		443		222
Year four		143		143		139
Year five		65		65		137
Prior		143		143		75
Revolving Loans		2,340		2,340		2,398
Revolving Loans Converted to Term		14		14		15
Total loans, net		4,086		4,086		4,271
Gross charge-offs
Year one				34		75
Year two				12		23
Year three				13		18
Year four				8		14
Year five				4		14
Prior				6		8
Revolving Loans				6		11
Revolving Loans Converted to Term						1
Total				83		164
Other consumer | Using FICO Credit Metric
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		382		382		693
Year two		539		539		476
Year three		348		348		189
Year four		125		125		91
Year five		52		52		66
Prior		49		49		41
Revolving Loans		235		235		249
Revolving Loans Converted to Term		4		4		5
Total loans, net		1,734		1,734		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		123		123		241
Year two		190		190		127
Year three		90		90		47
Year four		30		30		21
Year five		11		11		14
Prior		12		12		11
Revolving Loans		37		37		39
Revolving Loans Converted to Term		1		1		1
Total loans, net		494		494		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		156		156		286
Year two		205		205		157
Year three		109		109		54
Year four		36		36		26
Year five		14		14		17
Prior		13		13		11
Revolving Loans		75		75		80
Revolving Loans Converted to Term		1		1		1
Total loans, net		609		609		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		101		101		147
Year two		114		114		140
Year three		104		104		57
Year four		37		37		27
Year five		16		16		21
Prior		14		14		11
Revolving Loans		82		82		87
Revolving Loans Converted to Term		1		1		2
Total loans, net		469		469		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		2		2		19
Year two		30		30		52
Year three		45		45		31
Year four		22		22		17
Year five		11		11		14
Prior		10		10		8
Revolving Loans		41		41		43
Revolving Loans Converted to Term		1		1		1
Total loans, net		162		162		185
Other consumer | Other internal credit metrics
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one		7		7		19
Year two		10		10		97
Year three		95		95		33
Year four		18		18		48
Year five		13		13		71
Prior		94		94		34
Revolving Loans		2,105		2,105		2,149
Revolving Loans Converted to Term		10		10		10
Total loans, net		$ 2,352		$ 2,352		$ 2,461

[1] Our consolidated assets included the following for which we have elected the fair value option: Loans held for sale of $0.9 billion, Loans held for investment of $1.2 billion and Other assets of $0.1 billion at June 30, 2024. Comparable amounts at December 31, 2023 were $0.7 billion, $1.2 billion and $0.1 billion, respectively.