Commitments and Contingencies - MGP, Landfill and Disposal Sites (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($) Period Plan
Gas Trading Litigation [Member]
Loss Contingencies [Line Items]
Loss Contingency, Pending Claims, Number | Plan	2
Other MGP, Landfill, or Disposal Sites
Loss Contingencies [Line Items]
Number of identified MGP sites under current investigation and/or remediation	2
Maximum [Member] | Denver MGP Site [Member]
Loss Contingencies [Line Items]
Future environmental investigation, remediation or mitigation | $	$ 9.3
Time period of future environmental, investigation, remediation and mitigation measures | Period	15