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
Acquisition Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	$ 320	$ 329	$ 326	$ 322
Costs incurred	36	43	85	100
Amortization	(56)	(51)	(111)	(101)
End of period balance	300	321	300	321
Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	220	198	221	187
Costs incurred	34	44	70	78
Amortization	(35)	(35)	(72)	(58)
End of period balance	$ 219	$ 207	$ 219	$ 207