Asset Quality (Summary of TDRs) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings (TDRs)	$ 2,351	$ 2,583
Nonperforming [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings (TDRs)	1,119	1,370
Accruing [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings (TDRs)	1,232	1,213
Total commercial lending [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings (TDRs)	434	542
Total consumer lending [Member]
Financing Receivable, Modifications [Line Items]
Troubled debt restructurings (TDRs)	$ 1,917	$ 2,041