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		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 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	$ 122,819		$ 122,819		$ 124,500
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	799		799		841
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	257	$ 216	717	$ 552
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	118,871		118,871		118,944
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	781		781		822
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	253	213	705	544
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	67,077		67,077		65,793
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	675		675		730
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	242	219	692	540
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	12,015		12,015		11,050
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	85		85		85
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	1	(6)	3	4
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	36,005		36,005		38,853
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	13		13		7
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	1	0	1	0
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	3,774		3,774		3,248
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	8		8		0
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	9	0	9	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	2,293		2,293		2,392
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	14		14		13
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	3	2	9	6
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	2,293		2,293		2,392
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	14		14		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	1,655		1,655		3,164
Delinquent Amount at End of Period on Loans Managed and Securitized or Asset-backed Financing Arrangement	4		4		$ 6
Net Credit Losses During Period on Loans Managed or Securitized or Asset-backed Financing Arrangement	$ 1	$ 1	$ 3	$ 2