Revenue Recognition - Contract Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Acquisition Costs
Capitalized Contract Cost
Beginning of period balance	$ 68	$ 81	$ 73	$ 86
Costs incurred	12	12	36	39
Amortization	(14)	(15)	(43)	(47)
End of period balance	66	78	66	78
Fulfillment Costs
Capitalized Contract Cost
Beginning of period balance	49	59	54	64
Costs incurred	7	6	19	18
Amortization	(9)	(8)	(26)	(25)
End of period balance	$ 47	$ 57	$ 47	$ 57