Revenue from Contracts with Customers - Contract Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Capitalized Cost To Fulfill Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	$ 339	$ 335
Additions	346	318
Amortization	(443)	(416)
Impairment	0	0
Foreign currency translation and other	(1)	(8)
Balance at end of period	241	229
Capitalized Cost To Obtain Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	184	171
Additions	13	12
Amortization	(12)	(12)
Impairment	0	0
Foreign currency translation and other	0	(4)
Balance at end of period	$ 185	$ 167