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