Revenue Recognition - Capitalized Contract Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Contract Acquisition Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	$ 84	$ 90	$ 86	$ 90
Costs incurred	13	13	27	29
Amortization	(16)	(16)	(32)	(32)
End of period balance	81	87	81	87
Contract Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	61	57	64	57
Costs incurred	6	15	12	19
Amortization	(8)	(12)	(17)	(16)
End of period balance	$ 59	$ 60	$ 59	$ 60