Securitizations and Variable Interest Entities (Schedule of Quantitative Information and Net Credit Losses about Securitized and Other Financial Assets Managed Together) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	$ 124,500	$ 116,486
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	841	721
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	812	614
On-Balance Sheet Loans [Member]
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	118,944	111,705
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	822	699
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	801	609
On-Balance Sheet Loans [Member] | Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	65,793	64,292
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	730	591
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	795	578
On-Balance Sheet Loans [Member] | Consumer Portfolio Segment [Member] | Residential Mortgage [Member]
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	11,050	9,773
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	85	108
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	7	31
On-Balance Sheet Loans [Member] | Commercial Portfolio Segment [Member] | Automobile Loan [Member]
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	38,853	34,895
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	7	0
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	1	3
On-Balance Sheet Loans [Member] | Commercial Portfolio Segment [Member] | Other Financing Receivables [Member]
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	3,248	2,745
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	0	0
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	(2)	(3)
Off-Balance Sheet Loans [Member]
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	2,392	2,529
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	13	9
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	8	5
Off-Balance Sheet Loans [Member] | Consumer Portfolio Segment [Member] | Automobile Loan [Member]
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	2,392	2,529
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	13	9
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	8	5
Whole-Loan Transactions [Member]
Quantitative Information about Securitized and Other Financial Assets Managed Together [Line Items]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement	3,164	2,252
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	6	13
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	$ 3	$ 0