Finance Receivables and Loans, Net (Allowance for Credit Losses on Financing Receivables) (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment				$ 87		$ 87
Financing receivable, allowance for credit losses, collectively evaluated for impairment				1,190		1,190
Loans and leases receivable, gross	$ 118,028			128,609	$ 118,028	128,609	$ 128,231
Financing receivable, individually evaluated for impairment				906		906
Financing receivable, collectively evaluated for impairment				127,703		127,703
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(3,354)		$ (1,263)	(1,282)	(1,263)	(1,242)
Allowance for loan and lease losses, charge-offs	(279)			(393)	(954)	(1,071)
Allowance for loan and lease losses, recoveries	157			126	388	385
Allowance for loan and lease losses, net charge-offs	(122)			(267)	(566)	(686)
Provision for loan losses	147	$ 287		263	1,337	722
Allowance for Loan and Lease Losses, Adjustments, Other	0			(1)	(1)	(1)
Allowance for loan losses	(3,379)	(3,354)		(1,277)	(3,379)	(1,277)
Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses			(2,609)		(2,609)
Additional provision expense due to to macroeconomic and other factors
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	(34)	128	602
Increase in provision expense due to portfolio growth
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses	(59)
Consumer portfolio segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, gross	90,160				90,160		89,924
Consumer portfolio segment | Automotive loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment				37		37
Financing receivable, allowance for credit losses, collectively evaluated for impairment				1,053		1,053
Loans and leases receivable, gross	73,761			73,071	73,761	73,071	72,390
Financing receivable, individually evaluated for impairment				514		514
Financing receivable, collectively evaluated for impairment				72,557		72,557
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(2,963)		(1,075)	(1,078)	(1,075)	(1,048)
Allowance for loan and lease losses, charge-offs	(269)			(374)	(887)	(1,027)
Allowance for loan and lease losses, recoveries	152			121	371	368
Allowance for loan and lease losses, net charge-offs	(117)			(253)	(516)	(659)
Provision for loan losses	134			264	1,088	701
Allowance for Loan and Lease Losses, Adjustments, Other	2			1	1	0
Allowance for loan losses	(2,982)	(2,963)		(1,090)	(2,982)	(1,090)
Consumer portfolio segment | Automotive loan | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses			(2,409)		(2,409)
Consumer portfolio segment | Real estate-backed loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment				18		18
Financing receivable, allowance for credit losses, collectively evaluated for impairment				26		26
Loans and leases receivable, gross	16,072			17,010	16,072	17,010	17,322
Financing receivable, individually evaluated for impairment				213		213
Financing receivable, collectively evaluated for impairment				16,797		16,797
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(42)		(46)	(49)	(46)	(53)
Allowance for loan and lease losses, charge-offs	(4)			(3)	(9)	(11)
Allowance for loan and lease losses, recoveries	5			5	14	17
Allowance for loan and lease losses, net charge-offs	1			2	5	6
Provision for loan losses	(3)			(5)	(5)	(13)
Allowance for Loan and Lease Losses, Adjustments, Other	(1)			(2)	(1)	(2)
Allowance for loan losses	(39)	(42)		(44)	(39)	(44)
Consumer portfolio segment | Real estate-backed loan | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses			(40)		(40)
Consumer portfolio segment | Other
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(49)		(9)		(9)
Allowance for loan and lease losses, charge-offs	(2)				(11)
Allowance for loan and lease losses, recoveries	0				1
Allowance for loan and lease losses, net charge-offs	(2)				(10)
Provision for loan losses	20				51
Allowance for Loan and Lease Losses, Adjustments, Other	0				1
Allowance for loan losses	(67)	(49)			(67)
Consumer portfolio segment | Other | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses			(25)		(25)
Commercial portfolio segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment				32		32
Financing receivable, allowance for credit losses, collectively evaluated for impairment				111		111
Loans and leases receivable, gross	27,868			38,528	27,868	38,528	38,307
Financing receivable, individually evaluated for impairment				179		179
Financing receivable, collectively evaluated for impairment				38,349		38,349
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(300)		(133)	(155)	(133)	(141)
Allowance for loan and lease losses, charge-offs	(4)			(16)	(47)	(33)
Allowance for loan and lease losses, recoveries	0			0	2	0
Allowance for loan and lease losses, net charge-offs	(4)			(16)	(45)	(33)
Provision for loan losses	(4)			4	203	34
Allowance for Loan and Lease Losses, Adjustments, Other	(1)			0	(2)	1
Allowance for loan losses	(291)	$ (300)		$ (143)	(291)	$ (143)
Commercial portfolio segment | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses			(135)		(135)
Commercial portfolio segment | Automotive loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, gross	17,886				17,886		28,332
Commercial portfolio segment | Real estate-backed loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, gross	$ 4,851				4,851		$ 4,961
Accounting Standards Update 2016-13 | Retained Earnings | Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses			(1,346)		(1,346)
Accounting Standards Update 2016-13 | Retained Earnings | Consumer portfolio segment | Automotive loan | Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses			(1,334)		(1,334)
Accounting Standards Update 2016-13 | Retained Earnings | Consumer portfolio segment | Real estate-backed loan | Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses			6		6
Accounting Standards Update 2016-13 | Retained Earnings | Consumer portfolio segment | Other | Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses			(16)		(16)
Accounting Standards Update 2016-13 | Retained Earnings | Commercial portfolio segment | Revision of Prior Period, Accounting Standards Update, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses			$ (2)		$ (2)