Finance Receivables and Loans, Net (Allowance for Credit Losses on Financing Receivables) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance	$ 3,126	$ 3,354	$ 3,283	$ 1,263
Charge-offs	(218)	(279)	(723)	(954)
Recoveries	164	157	557	388
Net charge-offs	(54)	(122)	(166)	(566)
Provision for credit losses	76	147	31	1,337
Other		0		(1)
Allowance, ending balance	3,148	3,379	3,148	3,379
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance				1,346
Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance				2,609
Consumer | Automotive
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance	2,802	2,963	2,902	1,075
Charge-offs	(211)	(269)	(678)	(887)
Recoveries	160	152	535	371
Net charge-offs	(51)	(117)	(143)	(516)
Provision for credit losses	59	134	51	1,088
Other		2		1
Allowance, ending balance	2,810	2,982	2,810	2,982
Consumer | Automotive | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance				1,334
Consumer | Automotive | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance				2,409
Consumer | Mortgage/Real Estate
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance	24	42	33	46
Charge-offs	(2)	(4)	(6)	(9)
Recoveries	4	5	10	14
Net charge-offs	2	1	4	5
Provision for credit losses	(1)	(3)	(12)	(5)
Other		(1)		(1)
Allowance, ending balance	25	39	25	39
Consumer | Mortgage/Real Estate | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance				(6)
Consumer | Mortgage/Real Estate | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance				40
Consumer | Other
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance	72	49	73	9
Charge-offs	(5)	(2)	(18)	(11)
Recoveries	0	0	1	1
Net charge-offs	(5)	(2)	(17)	(10)
Provision for credit losses	19	20	30	51
Other		0		1
Allowance, ending balance	86	67	86	67
Finance receivables, fair value	8	8	8	8	$ 8	$ 8	$ 8	$ 11
Consumer | Other | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance				16
Consumer | Other | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance				25
Commercial
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance	228	300	275	133
Charge-offs	0	(4)	(21)	(47)
Recoveries	0	0	11	2
Net charge-offs	0	(4)	(10)	(45)
Provision for credit losses	(1)	(4)	(38)	203
Other		(1)		(2)
Allowance, ending balance	$ 227	$ 291	$ 227	291
Commercial | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance				2
Commercial | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance, beginning balance				$ 135