Revenue from Contracts with Customers - Contract Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Capitalized Cost To Fulfill Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	$ 193	$ 216	$ 335	$ 329
Additions	291	326	883	1,008
Amortization	(266)	(299)	(995)	(1,095)
Impairment	0	0	0	0
Foreign currency translation and other	2	(4)	(3)	(3)
Balance at end of period	220	239	220	239
Capitalized Cost To Obtain Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	172	161	171	156
Additions	15	14	43	40
Amortization	(12)	(11)	(35)	(33)
Impairment	0	0	0	0
Foreign currency translation and other	1	(1)	(3)	0
Balance at end of period	$ 176	$ 163	$ 176	$ 163