Revenue Recognition - Capitalized Contract Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Contract Acquisition Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	$ 86	$ 90
Costs incurred	14	16
Amortization	(16)	(16)
End of period balance	84	90
Contract Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	64	57
Costs incurred	6	4
Amortization	(9)	(4)
End of period balance	$ 61	$ 57