Revenue Recognition - Capitalized Contract Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Contract Acquisition Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	$ 73	$ 34	$ 64	$ 13
Costs incurred	13	16	42	42
Amortization	(12)	(5)	(32)	(10)
End of period balance	74	45	74	45
Contract Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	106	52	84	14
Costs incurred	26	22	77	69
Amortization	(17)	(8)	(46)	(17)
End of period balance	$ 115	$ 66	$ 115	$ 66