Variable Interest Entities (Aggregate Assets, Liabilities and Maximum Exposure to Loss) (Details) - Variable Interest Entity, Not Primary Beneficiary [Member] - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Variable Interest Entity [Line Items]
Aggregate assets	$ 161	$ 82
Aggregate liabilities	84	40
Maximum exposure to loss	170	107
LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Aggregate assets	104	45
Aggregate liabilities	84	40
Maximum exposure to loss	104	45
Other CRA Investments [Member]
Variable Interest Entity [Line Items]
Aggregate assets	57	37
Maximum exposure to loss	$ 66	$ 62