Revenue Recognition - Capitalized 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 [Roll Forward]
Beginning of period balance	$ 271	$ 300	$ 289	$ 326
Costs incurred	43	45	132	130
Amortization	(51)	(53)	(158)	(164)
Reclassified as held for sale	(35)	0	(35)	0
End of period balance	228	292	228	292
Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	217	219	216	221
Costs incurred	37	35	112	105
Amortization	(37)	(37)	(111)	(109)
Reclassified as held for sale	(31)	0	(31)	0
End of period balance	$ 186	$ 217	$ 186	$ 217