Income Taxes Schedule of Unrecognized Tax Benefits Roll Forward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits	$ 217	$ 208	$ 195	$ 235
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions	65	30	28
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions	1	1	9
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	12	20	5
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	29	19	46
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	38	12	7
Unrecognized Tax Benefits, Increase (Decrease) Resulting from Foreign Currency Translation	$ 0	$ (5)	$ (11)