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Finance Receivables and Loans, Net (Allowance for Credit Losses on Financing Receivables) (Details) - USD ($) $ in Millions		3 Months Ended
	Jan. 01, 2020	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment			$ 126
Financing receivable, allowance for credit losses, collectively evaluated for impairment			1,162
Loans and leases receivable, gross		$ 128,139	130,055	$ 128,231
Financing receivable, individually evaluated for impairment			997
Financing receivable, collectively evaluated for impairment			129,058
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	$ (1,263)	(1,263)	(1,242)
Allowance for loan and lease losses, charge-offs		(384)	(360)
Allowance for loan and lease losses, recoveries		118	123
Allowance for loan and lease losses, net charge-offs		(266)	(237)
Provision for loan losses		903	282
Allowance for Loan and Lease Losses, Adjustments, Other		(1)	1
Allowance for loan losses	(2,609)	(3,245)	(1,288)
Provision for credit losses		903	282
Additional provision expense due to COVID 19
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses		602
Consumer portfolio segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, gross		90,066		89,924
Consumer portfolio segment \| Fair value \| Finance receivables and loans, net
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Loans receivable, fair value		10		11
Consumer portfolio segment \| Automotive loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment			46
Financing receivable, allowance for credit losses, collectively evaluated for impairment			1,024
Loans and leases receivable, gross		72,832	71,553	72,390
Financing receivable, individually evaluated for impairment			501
Financing receivable, collectively evaluated for impairment			71,052
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(1,075)	(1,075)	(1,048)
Allowance for loan and lease losses, charge-offs		(373)	(352)
Allowance for loan and lease losses, recoveries		111	118
Allowance for loan and lease losses, net charge-offs		(262)	(234)
Provision for loan losses		685	257
Allowance for Loan and Lease Losses, Adjustments, Other		1	(1)
Allowance for loan losses	(2,409)	(2,833)	(1,070)
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			22
Financing receivable, allowance for credit losses, collectively evaluated for impairment			30
Loans and leases receivable, gross		17,010	17,658	17,322
Financing receivable, individually evaluated for impairment			227
Financing receivable, collectively evaluated for impairment			17,431
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(46)	(46)	(53)
Allowance for loan and lease losses, charge-offs		(3)	(3)
Allowance for loan and lease losses, recoveries		5	5
Allowance for loan and lease losses, net charge-offs		2	2
Provision for loan losses		(3)	(3)
Allowance for Loan and Lease Losses, Adjustments, Other		0	0
Allowance for loan losses	(40)	(39)	(52)
Consumer portfolio segment \| Other
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(9)	(9)
Allowance for loan and lease losses, charge-offs		(5)
Allowance for loan and lease losses, recoveries		1
Allowance for loan and lease losses, net charge-offs		(4)
Provision for loan losses		25
Allowance for Loan and Lease Losses, Adjustments, Other		(1)
Allowance for loan losses	(25)	(45)
Commercial portfolio segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment			58
Financing receivable, allowance for credit losses, collectively evaluated for impairment			108
Loans and leases receivable, gross		38,073	40,844	38,307
Financing receivable, individually evaluated for impairment			269
Financing receivable, collectively evaluated for impairment			40,575
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(133)	(133)	(141)
Allowance for loan and lease losses, charge-offs		(3)	(5)
Allowance for loan and lease losses, recoveries		1	0
Allowance for loan and lease losses, net charge-offs		(2)	(5)
Provision for loan losses		196	28
Allowance for Loan and Lease Losses, Adjustments, Other		(1)	2
Allowance for loan losses	(135)	(328)	$ (166)
Commercial portfolio segment \| Automotive loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, gross		27,394		28,332
Commercial portfolio segment \| Real estate-backed loan
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and leases receivable, gross		$ 4,801		$ 4,961
Accounting Standards Update 2016-13
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for Loan and Lease Losses, Adjustments, Other	1,300
Accounting Standards Update 2016-13 \| Retained Earnings
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(1,346)
Accounting Standards Update 2016-13 \| Retained Earnings \| Consumer portfolio segment \| Automotive loan
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(1,334)
Accounting Standards Update 2016-13 \| Retained Earnings \| Consumer portfolio segment \| Real estate-backed loan
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(6)
Accounting Standards Update 2016-13 \| Retained Earnings \| Consumer portfolio segment \| Other
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(16)
Accounting Standards Update 2016-13 \| Retained Earnings \| Commercial portfolio segment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	$ (2)