Revenue - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Revenue, Contract Assets, Liabilities and Costs[Line Items]
Contract liabilities	$ 135		$ 135		$ 130
Contract liability amortization period (months)			30 months
Deferred incremental direct costs, amortization period (years)	4 years		4 years
Deferred incremental direct costs net of accumulated amortization	$ 133		$ 133		145
Contract Fulfillment Costs and Inducements
Revenue, Contract Assets, Liabilities and Costs[Line Items]
Capitalized contract costs, amounts deferred	16		16		$ 13
Capitalized contract costs, amortization	$ 2	$ 1	$ 5	$ 3