Basis of Presentation - Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Contract Acquisition Costs
Deferred contract costs	$ 163	$ 153
Minimum [Member]
Contract Acquisition Costs
Deferred revenue recognition period	1 month
Contract amortization period	5 years
Maximum [Member]
Contract Acquisition Costs
Deferred revenue recognition period	3 months
Contract amortization period	13 years
Deferred Sales Incentives [Member]
Contract Acquisition Costs
Deferred contract costs	$ 118	$ 117