Debt - Credit Facility (Details) - USD ($)	3 Months Ended		12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Line of Credit Facility [Line Items]
Loss on extinguishment of debt	$ 22,000,000	$ 32,000,000	$ 22,000,000	$ 37,000,000	$ 19,000,000
Debt issuance cost		6,000,000	11,000,000	6,000,000
Line of credit
Line of Credit Facility [Line Items]
Maximum borrowing limit		$ 180,000,000	220,000,000	$ 180,000,000
Loss on extinguishment of debt			1,000,000
Debt issuance cost			1,000,000
Current borrowing capacity			155,000,000
Letters of credit outstanding			$ 29,000,000