Finance Receivables and Loans, Net (Financing Receivable Credit Quality Indicators) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	$ 130,055	$ 129,926	$ 125,327
Consumer portfolio segment | Consumer loan
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	89,211	87,240
Consumer portfolio segment | Consumer loan | Performing financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	88,493	86,497
Consumer portfolio segment | Consumer loan | Nonperforming financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	718	743
Consumer portfolio segment | Automobile loan
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	71,553	70,539	69,318
Consumer portfolio segment | Automobile loan | Performing financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	70,910	69,875
Consumer portfolio segment | Automobile loan | Nonperforming financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	643	664
Consumer portfolio segment | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	17,658	16,701	$ 14,683
Consumer portfolio segment | Residential mortgage | Performing financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	17,583	16,622
Consumer portfolio segment | Residential mortgage | Nonperforming financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	75	79
Consumer portfolio segment | Mortgage Finance
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	16,225	15,155
Consumer portfolio segment | Mortgage Finance | Performing financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	16,212	15,146
Consumer portfolio segment | Mortgage Finance | Nonperforming financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	13	9
Consumer portfolio segment | Mortgage - Legacy
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	1,433	1,546
Consumer portfolio segment | Mortgage - Legacy | Performing financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	1,371	1,476
Consumer portfolio segment | Mortgage - Legacy | Nonperforming financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	$ 62	$ 70