Revenue Recognition - 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
Beginning of period balance	$ 69	$ 84	$ 73	$ 86
Costs incurred	13	13	24	27
Amortization	(14)	(16)	(29)	(32)
End of period balance	68	81	68	81
Fulfillment Costs
Capitalized Contract Cost
Beginning of period balance	52	61	54	64
Costs incurred	6	6	12	12
Amortization	(9)	(8)	(17)	(17)
End of period balance	$ 49	$ 59	$ 49	$ 59