Credit Risk (Details) MMBbls in Millions, MMBTU in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) $ / MMBTU MMBTU MMBbls	Dec. 31, 2020 USD ($) $ / MMBTU MMBTU MMBbls	Dec. 31, 2019 USD ($)
Concentration Risk [Line Items]
Operating revenues	$ 1,340.1	$ 1,297.6	$ 1,295.2
Gas loaned to customers [Abstract]
Gas Balancing Measurement (in MMBtu) | MMBTU	7.4	11.2
Average Market Price Of Gas Assumed | $ / MMBTU	3.59	2.45
Gas Imbalance To Subsidiaries Asset Liability	$ 26.6	$ 27.4
Natural Gas Liquids Balancing Volume (in MMBbls) | MMBbls	0.0	0.0
Customer Concentration Risk
Concentration Risk [Line Items]
Operating revenues		$ 132.5
Concentration Risk, Benchmark Description	total operating revenues
Customer Concentration Risk | Revenue Benchmark
Concentration Risk [Line Items]
Concentration risk, percentage (approximately)		10.00%