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Finance Receivables and Loans, Net (Allowance for Credit Losses on Financing Receivables) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	$ (3,283)	$ (1,263)
Allowance for loan and lease losses, charge-offs	(308)	(384)
Allowance for loan and lease losses, recoveries	190	118
Allowance for loan and lease losses, net charge-offs	(118)	(266)
Provision for credit losses	(13)	903
Other	0	(1)
Allowance for loan losses	(3,152)	(3,245)
Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses		(2,609)
Consumer portfolio segment \| Automotive loan
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(2,902)	(1,075)
Allowance for loan and lease losses, charge-offs	(284)	(373)
Allowance for loan and lease losses, recoveries	187	111
Allowance for loan and lease losses, net charge-offs	(97)	(262)
Provision for credit losses	4	685
Other	0	1
Allowance for loan losses	(2,809)	(2,833)
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)
Consumer portfolio segment \| Real estate-backed loan
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(33)	(46)
Allowance for loan and lease losses, charge-offs	(2)	(3)
Allowance for loan and lease losses, recoveries	3	5
Allowance for loan and lease losses, net charge-offs	1	2
Provision for credit losses	(7)	(3)
Other	(1)	0
Allowance for loan losses	(26)	(39)
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)
Consumer portfolio segment \| Other
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(73)	(9)
Allowance for loan and lease losses, charge-offs	(8)	(5)
Allowance for loan and lease losses, recoveries	0	1
Allowance for loan and lease losses, net charge-offs	(8)	(4)
Provision for credit losses	3	25
Other	1	(1)
Allowance for loan losses	(69)	(45)
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)
Consumer portfolio segment \| Other loan
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Loans receivable, fair value	8	10	$ 8	$ 11
Commercial portfolio segment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	(275)	(133)
Allowance for loan and lease losses, charge-offs	(14)	(3)
Allowance for loan and lease losses, recoveries	0	1
Allowance for loan and lease losses, net charge-offs	(14)	(2)
Provision for credit losses	(13)	196
Other	0	(1)
Allowance for loan losses	$ (248)	(328)
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)
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)
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)
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
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)
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)