Securitizations and Variable Interest Entities Securitizations and Variable Interest Entities (On-balance Sheet Variable Interest Entities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Securitization and Variable Interest Entities On-balance Sheet Variable Interest Entities [Line Items]
Loans and Leases Receivable, Gross	$ 122,893	$ 118,944
Loans and Leases Receivable, Net Amount	121,617	117,800
Property Subject to or Available for Operating Lease, Net	8,741	11,470
Other Assets	5,663	6,854
Assets	167,148	163,728	$ 158,581
Long-term Debt	44,226	54,128
Liabilities	153,654	150,411
Variable Interest Entity, Primary Beneficiary [Member]
Securitization and Variable Interest Entities On-balance Sheet Variable Interest Entities [Line Items]
Loans and Leases Receivable, Allowance	(136)	(173)
Loans and Leases Receivable, Net Amount	20,487	24,457
Property Subject to or Available for Operating Lease, Net	444	1,745
Other Assets	689	1,390
Assets	21,620	27,592
Long-term Debt	10,197	13,259
Accounts Payable and Accrued Liabilities, Noncurrent	9	12
Liabilities	10,206	13,271
Consumer Portfolio Segment [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Securitization and Variable Interest Entities On-balance Sheet Variable Interest Entities [Line Items]
Loans and Leases Receivable, Gross	8,186	8,929
Commercial Portfolio Segment [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Securitization and Variable Interest Entities On-balance Sheet Variable Interest Entities [Line Items]
Loans and Leases Receivable, Gross	$ 12,437	$ 15,701