Gas and Liquids Stored Underground and Gas and NGLs Receivables and Payables (Details) MMBbls in Millions, MMBTU in Millions, $ in Millions	Jun. 30, 2017 USD ($) $ / MMBTU MMBTU MMBbls	Dec. 31, 2016 MMBTU MMBbls
Gas Balancing Arrangements [Abstract]
Gas Balancing Volume Amount (in MMBtu) | MMBTU	11.0	13.6
Average Market Price of Gas Assumed | $ / MMBTU	2.85
Gas Imbalance to Subsidiaries Asset Liability | $	$ 31.4
Natural Gas Liquids Balancing Volume (in MMBbls) (Less than) | MMBbls	0.0	0.1