Securities - Proceeds from Sales of Securities AFS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Gross realized gains	$ 22	$ 23	$ 190
Gross realized losses	$ 1	$ 0	$ 3