Revenue from Contracts with Customers - Contract Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Capitalized Cost To Fulfill Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	$ 241	$ 229	$ 339	$ 335
Additions	336	274	682	592
Amortization	(357)	(313)	(800)	(729)
Impairment	0	0	0	0
Foreign currency translation and other	2	3	1	(5)
Balance at end of period	222	193	222	193
Capitalized Cost To Obtain Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	185	167	184	171
Additions	15	16	28	28
Amortization	(13)	(11)	(25)	(23)
Impairment	0	0	0	0
Foreign currency translation and other	(12)	0	(12)	(4)
Balance at end of period	$ 175	$ 172	$ 175	$ 172