Revenue Recognition - Capitalized Contract Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Acquisition Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	$ 279	$ 320	$ 289	$ 326
Costs incurred	45	36	89	85
Amortization	(53)	(56)	(107)	(111)
End of period balance	271	300	271	300
Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	216	220	216	221
Costs incurred	38	34	75	70
Amortization	(37)	(35)	(74)	(72)
End of period balance	$ 217	$ 219	$ 217	$ 219