Asset Quality (Summary of TDRs) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings (TDRs)	$ 2,391	$ 2,351
Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings (TDRs)	1,172	1,119
Accruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings (TDRs)	1,219	1,232
Total commercial lending [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings (TDRs)	500	434
Total consumer lending [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings (TDRs)	$ 1,891	$ 1,917