Investment Securities (Investment Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest and Dividend Income, Securities, Operating, Available-for-sale	$ 418	$ 381	$ 367
Taxable interest	375	340	336
Taxable dividends	17	23	20
Interest and dividends exempt from U.S. federal income tax	19	18	11
Interest and Dividend Income, Securities, Operating, Available-for-sale	418	$ 381	$ 367
Excludes Other Earning Assets [Member]
Interest and Dividend Income, Securities, Operating, Available-for-sale	411
Interest and Dividend Income, Securities, Operating, Available-for-sale	$ 411