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	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
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	$ 125,154		$ 125,154		$ 124,500
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	692		692		841
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	203	$ 155	460	$ 336
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	120,545		120,545		118,944
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	676		676		822
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	199	152	452	331
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	66,774		66,774		65,793
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	586		586		730
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	199	148	450	321
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	11,297		11,297		11,050
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	82		82		85
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	0	4	2	10
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	38,840		38,840		38,853
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	8		8		7
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	3,634		3,634		3,248
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	0		0		0
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	2,662		2,662		2,392
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	13		13		13
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	3	2	6	4
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	2,662		2,662		2,392
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	13		13		13
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	1,947		1,947		3,164
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	3		3		$ 6
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	$ 1	$ 1	$ 2	$ 1