Other Long-term Liabilities, Components of Deferred Revenue (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Deferred Revenue Arrangement [Line Items]
Total deferred revenue	$ 135.2	$ 136.2
Channelview Splitter [Member]
Deferred Revenue Arrangement [Line Items]
Total deferred revenue	86.0	86.0
Gas Contract Amendment [Member]
Deferred Revenue Arrangement [Line Items]
Total deferred revenue	44.1	44.7
Other Deferred Revenue [Member]
Deferred Revenue Arrangement [Line Items]
Total deferred revenue	$ 5.1	$ 5.5