Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Foreign currency transaction losses	$ 5	$ 3	$ 6
Foreign currency transaction and translation
Cumulative translation loss adjustments	1,000	1,000
Investments
Cost Method Investments	2	2
Depreciation expense	179	171	172
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	803	784	$ 601
Intangible Assets, Net (Excluding Goodwill)	$ 493	$ 502
Building | Minimum
Property, Plant and Equipment [Line Items]
Useful life	25 years
Building | Maximum
Property, Plant and Equipment [Line Items]
Useful life	50 years
Other Capitalized Property Plant and Equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life	2 years
Other Capitalized Property Plant and Equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life	25 years