Revenue from Contracts with Customers - Contract Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Capitalized Cost To Fulfill Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	$ 236	$ 240	$ 329	$ 298
Additions	336	341	682	711
Amortization	(357)	(353)	(796)	(785)
Impairment	0	0	0	0
Foreign currency and other	1	(12)	1	(8)
Balance at end of period	216	216	216	216
Capitalized Cost To Obtain Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	155	144	156	145
Additions	17	13	26	21
Amortization	(11)	(11)	(22)	(21)
Impairment	0	0	0	0
Foreign currency and other	0	(2)	1	(1)
Balance at end of period	$ 161	$ 144	$ 161	$ 144