Gas and Liquids Stored Underground and Gas and NGLs Receivables and Payables (Details) MMBbls in Millions, MMBTU in Millions, $ in Millions	Jun. 30, 2019 USD ($) $ / MMBTU MMBTU MMBbls	Dec. 31, 2018 USD ($) $ / MMBTU MMBTU MMBbls
Gas Balancing Arrangements [Abstract]
Gas Balancing Measurement (in MMBtu) | MMBTU	19.5	13.5
Average Market Price of Gas Assumed | $ / MMBTU	2.22	3.68
Gas Imbalance to Subsidiaries Asset Liability | $	$ 43.3	$ 49.7
Natural Gas Liquids Balancing Volume (in MMBbls) | MMBbls	0.0	0.0