Revenue from Contracts with Customers - Contract Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Capitalized Cost To Fulfill Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	$ 329	$ 298
Additions	346	1,504
Amortization	(439)	(1,465)
Impairment	0	0
Foreign currency and other	0	(8)
Balance at end of period	236	329
Capitalized Cost To Obtain Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	156	145
Additions	9	53
Amortization	(11)	(41)
Impairment	0	0
Foreign currency and other	1	(1)
Balance at end of period	$ 155	$ 156