Revenue Recognition - Capitalized Contract Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Acquisition Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	$ 77	$ 73	$ 79	$ 64
Costs incurred	14	13	44	42
Amortization	(15)	(12)	(47)	(32)
End of period balance	76	74	76	74
Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	122	106	121	84
Costs incurred	21	26	65	77
Amortization	(22)	(17)	(65)	(46)
End of period balance	$ 121	$ 115	$ 121	$ 115