Revenue from Contracts with Customers - Contract Assets Rollforward (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Capitalized Cost To Fulfill Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	$ 298
Additions	1,504
Amortization	(1,465)
Impairment	0
Foreign currency translation and other	(8)
Balance at end of period	329
Capitalized Cost To Obtain Customer Contracts
Change in Capitalized Contract Costs
Balance at beginning of period	145
Additions	53
Amortization	(41)
Impairment	0
Foreign currency translation and other	(1)
Balance at end of period	$ 156