Revenue Recognition - Capitalized Contract Costs (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
Beginning of period balance	$ 81	$ 87	$ 86	$ 90
Costs incurred	12	15	39	44
Amortization	(15)	(15)	(47)	(47)
End of period balance	78	87	78	87
Fulfillment Costs
Capitalized Contract Cost
Beginning of period balance	59	60	64	57
Costs incurred	6	10	18	29
Amortization	(8)	(8)	(25)	(24)
End of period balance	$ 57	$ 62	$ 57	$ 62