Revenue Recognition - Contract Cost (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	$ 75	$ 77	$ 78	$ 79
Costs incurred	15	14	44	44
Amortization	(14)	(15)	(46)	(47)
Reclassified as held for sale	0	0	0	0
End of period balance	76	76	76	76
Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	124	122	122	121
Costs incurred	22	21	68	65
Amortization	(21)	(22)	(65)	(65)
Reclassified as held for sale	(27)	0	(27)	0
End of period balance	$ 98	$ 121	$ 98	$ 121