Revenue from Contracts with Customers - Contract Cost Balances (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Capitalized Contract Cost [Line Items]
Current contract cost assets	$ 47,000,000	$ 47,000,000	$ 62,000,000	$ 62,000,000
Non-current contract cost assets	90,000,000	90,000,000	$ 85,000,000	$ 0
Contract cost, amortization	$ 11,000,000	$ 23,000,000
Minimum
Capitalized Contract Cost [Line Items]
Capitalized contract cost, amortization period		1 year
Maximum
Capitalized Contract Cost [Line Items]
Capitalized contract cost, amortization period		4 years