Revenue Recognition - Capitalized Contract Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Contract Acquisition Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	$ 74	$ 26	$ 64	$ 13
Costs incurred	11	11	29	26
Amortization	(12)	(3)	(20)	(5)
End of period balance	73	34	73	34
Contract Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	97	35	84	14
Costs incurred	25	24	51	47
Amortization	(16)	(7)	(29)	(9)
End of period balance	$ 106	$ 52	$ 106	$ 52