Revenue from Contracts with Customers - Contract Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Capitalized Cost To Fulfill Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	$ 216	$ 216	$ 329	$ 298
Additions	326	332	1,008	1,043
Amortization	(299)	(305)	(1,095)	(1,090)
Impairment	0	0	0	0
Foreign currency translation and other	(4)	5	(3)	(3)
Balance at end of period	239	248	239	248
Capitalized Cost To Obtain Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	161	144	156	145
Additions	14	16	40	37
Amortization	(11)	(9)	(33)	(30)
Impairment	0	0	0	0
Foreign currency translation and other	(1)	(1)	0	(2)
Balance at end of period	$ 163	$ 150	$ 163	$ 150