Finance Receivables and Loans, Net (Financing Receivable Credit Quality Indicators) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	$ 126,605	$ 122,893	$ 118,871
Consumer portfolio segment | Consumer loan
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	86,501	81,821
Consumer portfolio segment | Consumer loan | Performing financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	85,782	81,101
Consumer portfolio segment | Consumer loan | Nonperforming financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	719	720
Consumer portfolio segment | Automobile loan
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	69,995	68,071	67,077
Consumer portfolio segment | Automobile loan | Performing financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	69,375	67,468
Consumer portfolio segment | Automobile loan | Nonperforming financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	620	603
Consumer portfolio segment | Residential mortgage
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	16,506	13,750	$ 12,015
Consumer portfolio segment | Residential mortgage | Performing financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	16,407	13,633
Consumer portfolio segment | Residential mortgage | Nonperforming financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	99	117
Consumer portfolio segment | Mortgage Finance
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	14,840	11,657
Consumer portfolio segment | Mortgage Finance | Performing financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	14,822	11,632
Consumer portfolio segment | Mortgage Finance | Nonperforming financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	18	25
Consumer portfolio segment | Mortgage - Legacy
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	1,666	2,093
Consumer portfolio segment | Mortgage - Legacy | Performing financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	1,585	2,001
Consumer portfolio segment | Mortgage - Legacy | Nonperforming financial instruments
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	$ 81	$ 92