Other Information (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Other Assets [Abstract]
Natural gas and NGLs inventory	$ 30.1	$ 17.4
Prepaid expenses and other	11.1	16.1
Natural gas and NGLs inventory, prepaid expenses and other	41.2	33.5
Other Liabilities [Abstract]
Accrued interest	35.6	34.2
Accrued wages and benefits, including taxes	30.4	19.0
Accrued ad valorem taxes	27.8	23.5
Capital expenditure accruals	48.8	64.6
Onerous performance obligations	15.2	15.9
Other	65.1	60.3
Other current liabilities	$ 222.9	$ 217.5