Commitment and Contingencies - Schedule of Estimated Accrued Costs (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021 USD ($) year
Minnesota and Indiana Gas Service Territories
Loss Contingencies [Line Items]
Liability recorded for environmental loss contingencies	$ 12
Minnesota and Indiana Gas Service Territories | Minimum
Loss Contingencies [Line Items]
Estimated remediation costs	$ 8
Years to resolve contingency | year	5
Minnesota and Indiana Gas Service Territories | Maximum
Loss Contingencies [Line Items]
Estimated remediation costs	$ 54
Years to resolve contingency | year	50
Minnesota Service Territory | CERC Corp
Loss Contingencies [Line Items]
Liability recorded for environmental loss contingencies	$ 7
Minnesota Service Territory | CERC Corp | Minimum
Loss Contingencies [Line Items]
Estimated remediation costs	$ 5
Years to resolve contingency | year	30
Minnesota Service Territory | CERC Corp | Maximum
Loss Contingencies [Line Items]
Estimated remediation costs	$ 32
Years to resolve contingency | year	50