Revenue Recognition - Capitalized Contract Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Acquisition Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	$ 326	$ 322
Costs incurred	49	57
Amortization	(55)	(50)
End of period balance	320	329
Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	221	187
Costs incurred	36	34
Amortization	(37)	(23)
End of period balance	$ 220	$ 198