Income Taxes (Schedule of Income (Loss) Before Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
United States	$ (783)	$ (1,449)	$ (2,384)
Foreign	329	285	(55)
Income from continuing operations before income taxes	$ (454)	$ (1,164)	$ (2,439)