Finance Receivables and Loans, Net (Allowance for Credit Losses on Financing Receivables) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	$ 1,288,000,000	$ 1,278,000,000	$ 1,242,000,000	$ 1,276,000,000
Allowance for loan and lease losses, charge-offs	(318,000,000)	(306,000,000)	(678,000,000)	(683,000,000)
Allowance for loan and lease losses, recoveries	136,000,000	126,000,000	259,000,000	244,000,000
Allowance for loan and lease losses, net charge-offs	(182,000,000)	(180,000,000)	(419,000,000)	(439,000,000)
Provision for loan losses	177,000,000	158,000,000	459,000,000	419,000,000
Allowance for Loan and Lease Losses, Adjustments, Other	(1,000,000)	1,000,000	0	1,000,000
Allowance for loan losses	1,282,000,000	1,257,000,000	1,282,000,000	1,257,000,000
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses, individually evaluated for impairment	111,000,000	93,000,000	111,000,000	93,000,000
Allowance for loan losses, collectively evaluated for impairment	1,171,000,000	1,164,000,000	1,171,000,000	1,164,000,000
Finance receivables and loans, net	129,210,000,000	125,544,000,000	129,210,000,000	125,544,000,000	$ 129,926,000,000
Finance receivables and loans, individually evaluated for impairment	912,000,000	906,000,000	912,000,000	906,000,000
Finance receivables and loans, collectively evaluated for impairment	128,298,000,000	124,638,000,000	128,298,000,000	124,638,000,000
Consumer portfolio segment
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Finance receivables and loans, net	90,698,000,000		90,698,000,000		87,240,000,000
Consumer portfolio segment | Automotive loan
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	1,070,000,000	1,066,000,000	1,048,000,000	1,066,000,000
Allowance for loan and lease losses, charge-offs	(301,000,000)	(296,000,000)	(653,000,000)	(661,000,000)
Allowance for loan and lease losses, recoveries	129,000,000	114,000,000	247,000,000	226,000,000
Allowance for loan and lease losses, net charge-offs	(172,000,000)	(182,000,000)	(406,000,000)	(435,000,000)
Provision for loan losses	180,000,000	168,000,000	437,000,000	421,000,000
Allowance for Loan and Lease Losses, Adjustments, Other	0	1,000,000	(1,000,000)	1,000,000
Allowance for loan losses	1,078,000,000	1,053,000,000	1,078,000,000	1,053,000,000
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses, individually evaluated for impairment	42,000,000	42,000,000	42,000,000	42,000,000
Allowance for loan losses, collectively evaluated for impairment	1,036,000,000	1,011,000,000	1,036,000,000	1,011,000,000
Finance receivables and loans, net	72,898,000,000	70,473,000,000	72,898,000,000	70,473,000,000	70,539,000,000
Finance receivables and loans, individually evaluated for impairment	496,000,000	480,000,000	496,000,000	480,000,000
Finance receivables and loans, collectively evaluated for impairment	72,402,000,000	69,993,000,000	72,402,000,000	69,993,000,000
Consumer portfolio segment | Real estate-backed loan
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	52,000,000	74,000,000	53,000,000	79,000,000
Allowance for loan and lease losses, charge-offs	(5,000,000)	(8,000,000)	(8,000,000)	(20,000,000)
Allowance for loan and lease losses, recoveries	7,000,000	6,000,000	12,000,000	12,000,000
Allowance for loan and lease losses, net charge-offs	2,000,000	(2,000,000)	4,000,000	(8,000,000)
Provision for loan losses	(5,000,000)	(4,000,000)	(8,000,000)	(3,000,000)
Allowance for Loan and Lease Losses, Adjustments, Other	0	(2,000,000)	0	(2,000,000)
Allowance for loan losses	49,000,000	66,000,000	49,000,000	66,000,000
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses, individually evaluated for impairment	20,000,000	24,000,000	20,000,000	24,000,000
Allowance for loan losses, collectively evaluated for impairment	29,000,000	42,000,000	29,000,000	42,000,000
Finance receivables and loans, net	17,800,000,000	15,131,000,000	17,800,000,000	15,131,000,000	16,701,000,000
Finance receivables and loans, individually evaluated for impairment	220,000,000	228,000,000	220,000,000	228,000,000
Finance receivables and loans, collectively evaluated for impairment	17,580,000,000	14,903,000,000	17,580,000,000	14,903,000,000
Commercial portfolio segment
Financing Receivable, Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses	166,000,000	138,000,000	141,000,000	131,000,000
Allowance for loan and lease losses, charge-offs	(12,000,000)	(2,000,000)	(17,000,000)	(2,000,000)
Allowance for loan and lease losses, recoveries	0	6,000,000	0	6,000,000
Allowance for loan and lease losses, net charge-offs	(12,000,000)	4,000,000	(17,000,000)	4,000,000
Provision for loan losses	2,000,000	(6,000,000)	30,000,000	1,000,000
Allowance for Loan and Lease Losses, Adjustments, Other	(1,000,000)	2,000,000	1,000,000	2,000,000
Allowance for loan losses	155,000,000	138,000,000	155,000,000	138,000,000
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses, individually evaluated for impairment	49,000,000	27,000,000	49,000,000	27,000,000
Allowance for loan losses, collectively evaluated for impairment	106,000,000	111,000,000	106,000,000	111,000,000
Finance receivables and loans, net	38,512,000,000	39,940,000,000	38,512,000,000	39,940,000,000	42,686,000,000
Finance receivables and loans, individually evaluated for impairment	196,000,000	198,000,000	196,000,000	198,000,000
Finance receivables and loans, collectively evaluated for impairment	38,316,000,000	$ 39,742,000,000	38,316,000,000	$ 39,742,000,000
Commercial portfolio segment | Automotive loan
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Finance receivables and loans, net	29,382,000,000		29,382,000,000		33,672,000,000
Commercial portfolio segment | Real estate-backed loan
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Finance receivables and loans, net	$ 4,777,000,000		$ 4,777,000,000		$ 4,809,000,000