Revenue from Contracts with Customers - Contract Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Capitalized Cost To Fulfill Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	$ 222	$ 193	$ 339	$ 335
Additions	340	291	1,022	883
Amortization	(310)	(266)	(1,110)	(995)
Impairment	0	0	0	0
Foreign currency translation and other	(3)	2	(2)	(3)
Balance at end of period	249	220	249	220
Capitalized Cost To Obtain Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	175	172	184	171
Additions	12	15	40	43
Amortization	(11)	(12)	(36)	(35)
Impairment	0	0	0	0
Foreign currency translation and other	(2)	1	(14)	(3)
Balance at end of period	$ 174	$ 176	$ 174	$ 176