Other Investments (Narrative) (Details) - RGC Midstream, LLC $ in Millions	1 Months Ended
	Apr. 30, 2018 USD ($) mi	Sep. 30, 2020 USD ($) debt_instrument	Nov. 30, 2019	Jun. 30, 2019 instrument_held	Jun. 30, 2019 debt_instrument	Oct. 31, 2015 Bcf
Investment [Line Items]
Number of notes		2		2	2
MVP Southgate Investment
Investment [Line Items]
Ownership percentage (less than)	1.00%
MVP Investment
Investment [Line Items]
Equity interest (as a percent)			1.03%			1.00%
Pipeline capacity (in bcf per day) | Bcf						2
MVP Investment | Minimum
Investment [Line Items]
Total project cost		$ 5,800.0
Total estimated investment		60.0
MVP Investment | Maximum
Investment [Line Items]
Total project cost		6,000.0
Total estimated investment		$ 62.0
MVP Southgate Investment
Investment [Line Items]
Length, planned natural gas pipeline (in miles) | mi	75
MVP Southgate Investment | Maximum
Investment [Line Items]
Total project cost	$ 500.0
Total estimated investment	$ 2.1