Equity Level 4 Preferred Stock & SE Warrants (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	Mar. 23, 2010	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Class of Stock [Line Items]
Depository shares, issued	23.0
Interest in mandatory convertible preferred stock series F represented by each depositary share	1/40th
Sale of depository shares price per share	$ 25
Net proceeds from issuance of depository shares	$ 556
Exercise price of warrant		$ 9.264	$ 9.388	$ 9.504
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Cumulative dividend on mandatory convertible preferred stock	7.25%
Preferred stock, liquidation preference per share	$ 1,000
Convertible preferred stock shares, Series F, reserved for future issuance					21.2