Finance Receivables and Loans, Net (Financing Receivable Credit Quality Indicators Consumer) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total finance receivables and loans	$ 114,471		$ 118,534
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total finance receivables and loans	95,052		89,202
Consumer | Excludes fair value option elected other loans
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	36,901		31,399
Year two, originated, fiscal year before current fiscal year	22,691		22,426
Year three, originated, two years before current fiscal year	14,924		14,509
Year four, originated, three years before current fiscal year	9,117		9,765
Year five, originated, four years before current fiscal year	5,603		5,143
Originated, more than five years before current fiscal year	5,519		5,604
Revolving loans	260		310
Revolving loans converted to term	29		38
Total finance receivables and loans	95,044		89,194
Consumer | Automotive
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	28,656		27,634
Year two, originated, fiscal year before current fiscal year	20,030		19,943
Year three, originated, two years before current fiscal year	13,735		12,730
Year four, originated, three years before current fiscal year	8,223		7,483
Year five, originated, four years before current fiscal year	4,394		3,953
Originated, more than five years before current fiscal year	2,723		1,925
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	77,761		73,668
Consumer | Mortgage/Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	7,621		3,444
Year two, originated, fiscal year before current fiscal year	2,489		2,425
Year three, originated, two years before current fiscal year	1,165		1,765
Year four, originated, three years before current fiscal year	888		2,277
Year five, originated, four years before current fiscal year	1,207		1,189
Originated, more than five years before current fiscal year	2,796		3,679
Revolving loans	260		310
Revolving loans converted to term	29		38
Total finance receivables and loans	16,455		15,127
Consumer | Mortgage Finance
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	7,621		3,444
Year two, originated, fiscal year before current fiscal year	2,489		2,425
Year three, originated, two years before current fiscal year	1,165		1,765
Year four, originated, three years before current fiscal year	888		2,277
Year five, originated, four years before current fiscal year	1,207		1,189
Originated, more than five years before current fiscal year	2,689		3,532
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	16,059		14,632
Consumer | Mortgage - Legacy
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	0		0
Year two, originated, fiscal year before current fiscal year	0		0
Year three, originated, two years before current fiscal year	0		0
Year four, originated, three years before current fiscal year	0		0
Year five, originated, four years before current fiscal year	0		0
Originated, more than five years before current fiscal year	107		147
Revolving loans	260		310
Revolving loans converted to term	29		38
Total finance receivables and loans	396		495
Consumer | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total finance receivables and loans	836		407
Finance receivables, fair value	8	$ 8	8	$ 8	$ 8	$ 11
Consumer | Other | Excludes fair value option elected other loans
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	624		321
Year two, originated, fiscal year before current fiscal year	172		58
Year three, originated, two years before current fiscal year	24		14
Year four, originated, three years before current fiscal year	6		5
Year five, originated, four years before current fiscal year	2		1
Originated, more than five years before current fiscal year	0		0
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	828		399
Current | Consumer | Automotive
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	28,365		27,255
Year two, originated, fiscal year before current fiscal year	19,572		19,204
Year three, originated, two years before current fiscal year	13,244		12,129
Year four, originated, three years before current fiscal year	7,877		7,060
Year five, originated, four years before current fiscal year	4,172		3,678
Originated, more than five years before current fiscal year	2,538		1,766
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	75,768		71,092
Current | Consumer | Mortgage Finance
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	7,542		3,432
Year two, originated, fiscal year before current fiscal year	2,485		2,410
Year three, originated, two years before current fiscal year	1,151		1,744
Year four, originated, three years before current fiscal year	862		2,254
Year five, originated, four years before current fiscal year	1,192		1,177
Originated, more than five years before current fiscal year	2,649		3,492
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	15,881		14,509
Current | Consumer | Mortgage - Legacy
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	0		0
Year two, originated, fiscal year before current fiscal year	0		0
Year three, originated, two years before current fiscal year	0		0
Year four, originated, three years before current fiscal year	0		0
Year five, originated, four years before current fiscal year	0		0
Originated, more than five years before current fiscal year	86		121
Revolving loans	252		303
Revolving loans converted to term	26		36
Total finance receivables and loans	364		460
Current | Consumer | Other | Excludes fair value option elected other loans
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	613		306
Year two, originated, fiscal year before current fiscal year	168		53
Year three, originated, two years before current fiscal year	24		13
Year four, originated, three years before current fiscal year	6		4
Year five, originated, four years before current fiscal year	2		1
Originated, more than five years before current fiscal year	0		0
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	813		377
Financing receivables, 30 to 59 days past due | Consumer | Automotive
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	224		281
Year two, originated, fiscal year before current fiscal year	325		466
Year three, originated, two years before current fiscal year	335		376
Year four, originated, three years before current fiscal year	238		264
Year five, originated, four years before current fiscal year	152		174
Originated, more than five years before current fiscal year	122		97
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	1,396		1,658
Financing receivables, 30 to 59 days past due | Consumer | Mortgage Finance
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	78		10
Year two, originated, fiscal year before current fiscal year	4		9
Year three, originated, two years before current fiscal year	10		10
Year four, originated, three years before current fiscal year	18		11
Year five, originated, four years before current fiscal year	12		7
Originated, more than five years before current fiscal year	23		16
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	145		63
Financing receivables, 30 to 59 days past due | Consumer | Mortgage - Legacy
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	0		0
Year two, originated, fiscal year before current fiscal year	0		0
Year three, originated, two years before current fiscal year	0		0
Year four, originated, three years before current fiscal year	0		0
Year five, originated, four years before current fiscal year	0		0
Originated, more than five years before current fiscal year	5		4
Revolving loans	4		2
Revolving loans converted to term	2		0
Total finance receivables and loans	11		6
Financing receivables, 30 to 59 days past due | Consumer | Other | Excludes fair value option elected other loans
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	5		9
Year two, originated, fiscal year before current fiscal year	2		3
Year three, originated, two years before current fiscal year	0		1
Year four, originated, three years before current fiscal year	0		0
Year five, originated, four years before current fiscal year	0		0
Originated, more than five years before current fiscal year	0		0
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	7		13
Financing receivables, 60 to 89 days past due | Consumer | Automotive
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	50		66
Year two, originated, fiscal year before current fiscal year	93		165
Year three, originated, two years before current fiscal year	102		129
Year four, originated, three years before current fiscal year	68		88
Year five, originated, four years before current fiscal year	41		55
Originated, more than five years before current fiscal year	32		32
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	386		535
Financing receivables, 60 to 89 days past due | Consumer | Mortgage Finance
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	1		1
Year two, originated, fiscal year before current fiscal year	0		1
Year three, originated, two years before current fiscal year	0		3
Year four, originated, three years before current fiscal year	0		2
Year five, originated, four years before current fiscal year	1		1
Originated, more than five years before current fiscal year	3		3
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	5		11
Financing receivables, 60 to 89 days past due | Consumer | Mortgage - Legacy
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	0		0
Year two, originated, fiscal year before current fiscal year	0		0
Year three, originated, two years before current fiscal year	0		0
Year four, originated, three years before current fiscal year	0		0
Year five, originated, four years before current fiscal year	0		0
Originated, more than five years before current fiscal year	2		2
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	2		2
Financing receivables, 60 to 89 days past due | Consumer | Other | Excludes fair value option elected other loans
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	4		4
Year two, originated, fiscal year before current fiscal year	1		1
Year three, originated, two years before current fiscal year	0		0
Year four, originated, three years before current fiscal year	0		1
Year five, originated, four years before current fiscal year	0		0
Originated, more than five years before current fiscal year	0		0
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	5		6
Financing receivables, 90 or more days past due | Consumer | Automotive
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	17		32
Year two, originated, fiscal year before current fiscal year	40		108
Year three, originated, two years before current fiscal year	54		96
Year four, originated, three years before current fiscal year	40		71
Year five, originated, four years before current fiscal year	29		46
Originated, more than five years before current fiscal year	31		30
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	211		383
Financing receivables, 90 or more days past due | Consumer | Mortgage Finance
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	0		1
Year two, originated, fiscal year before current fiscal year	0		5
Year three, originated, two years before current fiscal year	4		8
Year four, originated, three years before current fiscal year	8		10
Year five, originated, four years before current fiscal year	2		4
Originated, more than five years before current fiscal year	14		21
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	28		49
Financing receivables, 90 or more days past due | Consumer | Mortgage - Legacy
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	0		0
Year two, originated, fiscal year before current fiscal year	0		0
Year three, originated, two years before current fiscal year	0		0
Year four, originated, three years before current fiscal year	0		0
Year five, originated, four years before current fiscal year	0		0
Originated, more than five years before current fiscal year	14		20
Revolving loans	4		5
Revolving loans converted to term	1		2
Total finance receivables and loans	19		27
Financing receivables, 90 or more days past due | Consumer | Other | Excludes fair value option elected other loans
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated, current fiscal year	2		2
Year two, originated, fiscal year before current fiscal year	1		1
Year three, originated, two years before current fiscal year	0		0
Year four, originated, three years before current fiscal year	0		0
Year five, originated, four years before current fiscal year	0		0
Originated, more than five years before current fiscal year	0		0
Revolving loans	0		0
Revolving loans converted to term	0		0
Total finance receivables and loans	$ 3		$ 3