Finance Receivables and Loans, Net Finance Receivables and Loans, Net (Past Due Financing Receivables and Loans Commercial) (Details) $ in Millions	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)
Financing Receivable, Past Due [Line Items]
Finance receivables and loans, net	$ 128,139	$ 128,231	$ 130,055
Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	42	83
Financing receivable, recorded investment, current	38,031	38,224
Finance receivables and loans, net	38,073	38,307	$ 40,844
Automotive loan | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	38	62
Financing receivable, recorded investment, current	27,356	28,270
Finance receivables and loans, net	27,394	28,332
Other loan | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	0	17
Financing receivable, recorded investment, current	5,878	4,997
Finance receivables and loans, net	5,878	5,014
Real estate-backed loan | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	4	4
Financing receivable, recorded investment, current	4,797	4,957
Finance receivables and loans, net	4,801	4,961
Financing receivables, 30 to 59 days past due | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	0	34
Financing receivables, 30 to 59 days past due | Automotive loan | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	0	34
Financing receivables, 30 to 59 days past due | Other loan | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	0	0
Financing receivables, 30 to 59 days past due | Real estate-backed loan | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	0	0
Financing receivables, 60 to 89 days past due | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	0	0
Financing receivables, 60 to 89 days past due | Automotive loan | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	0	0
Financing receivables, 60 to 89 days past due | Other loan | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	0	0
Financing receivables, 60 to 89 days past due | Real estate-backed loan | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	0	0
Financing receivables, equal to greater than 90 days past due | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	42	49
Financing receivables, equal to greater than 90 days past due | Automotive loan | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	38	28
Financing receivables, equal to greater than 90 days past due | Other loan | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	0	17
Financing receivables, equal to greater than 90 days past due | Real estate-backed loan | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Financing receivable, recorded investment, past due	$ 4	$ 4
Operating Segments | Automotive Finance operations | Commercial portfolio segment
Financing Receivable, Past Due [Line Items]
Commercial automotive customers enrolling in program	2,270
Percent of customers enrolling in program	72.00%