Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Revenue, Contract Assets, Liabilities and Costs[Line Items]
Contract liabilities	$ 132		$ 116
Contract liability amortization period	30 months
Deferred incremental direct costs, amortization period	4 years
Incremental Direct Costs of Obtaining a Contract	$ 18	$ 17
Capitalized contract costs amortization reported in decrease (increase) in other current and long-term assets	23	24
Deferred incremental direct costs net of accumulated amortization	167		172
Contract Fulfillment Costs and Inducements
Revenue, Contract Assets, Liabilities and Costs[Line Items]
Capitalized contract costs, deferred	12		$ 12
Amortization of Capitalized Contract Fulfillment and Inducement Costs	$ 1	$ 1