Income Taxes (Unrecognized Tax Benefits Excluding Interest) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Abstract]
Unrecognized Tax Benefits, Beginning Balance	$ (286)	$ (317)
Additions for tax positions of prior years	(1)	(1)
Unrecognized Tax Benefits, Decreases Resulting from Prior Period Tax Positions	1
Unrecognized Tax Benefits, Reductions Resulting from Lapse of Applicable Statute of Limitations		42
Foreign currency translation	(20)	(10)
Unrecognized Tax Benefits, Ending Balance	$ (306)	$ (286)