Revenue - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Revenue, Contract Assets, Liabilities and Costs[Line Items]
Contract liabilities	$ 130		$ 130		$ 137
Contract liability amortization period			30 months
Deferred incremental direct costs, amortization period	4 years		4 years
Deferred incremental direct costs net of accumulated amortization	$ 145		$ 145		163
Contract Fulfillment Costs and Inducements
Revenue, Contract Assets, Liabilities and Costs[Line Items]
Capitalized contract costs, amounts deferred	12		12		$ 13
Capitalized contract costs, amortization	$ 1	$ 1	$ 3	$ 4