Income Taxes (Net Operating Loss Carryforwards) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Internal Revenue Service (IRS)
Operating Loss Carryforwards	$ 640	$ 759
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2032
State and Local Jurisdiction
Operating Loss Carryforwards	$ 1,776	$ 2,345
Operating Loss Carryforwards Earliest Expiration Date	2018
Operating Loss Carryforwards Latest Expiration Date	2036