Finance Receivables and Loans, Net (Schedule of Pass And Criticized Credit Quality Indicators of Finance Receivables) (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
Commercial portfolio segment | Commercial loan
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	40,104	41,072	$ 39,779
Commercial portfolio segment | Commercial loan | Pass
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	36,450	37,991
Commercial portfolio segment | Commercial loan | Criticized
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	3,654	3,081
Commercial portfolio segment | Commercial and industrial automotive
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	31,424	33,025
Commercial portfolio segment | Commercial and industrial automotive | Pass
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	28,789	30,982
Commercial portfolio segment | Commercial and industrial automotive | Criticized
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	2,635	2,043
Commercial portfolio segment | Commercial and industrial other
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	4,132	3,887
Commercial portfolio segment | Commercial and industrial other | Pass
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	3,328	2,986
Commercial portfolio segment | Commercial and industrial other | Criticized
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	804	901
Commercial portfolio segment | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	4,548	4,160
Commercial portfolio segment | Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	4,333	4,023
Commercial portfolio segment | Commercial real estate | Criticized
Financing Receivable, Recorded Investment [Line Items]
Finance receivables and loans, net	$ 215	$ 137