Variable Interest Entities (Aggregate Assets, Liabilities and Maximum Exposure to Loss) (Details) - Variable Interest Entity, Not Primary Beneficiary [Member] - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Aggregate assets	$ 249	$ 161
Aggregate liabilities	135	84
Maximum exposure to loss	269	170
LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Aggregate assets	189	104
Aggregate liabilities	135	84
Maximum exposure to loss	189	104
Other CRA Investments [Member]
Variable Interest Entity [Line Items]
Aggregate assets	60	57
Maximum exposure to loss	$ 80	$ 66