Commitments and Contingencies - Environmental Requirements - Water and Waste (Details) $ in Millions	3 Months Ended
	Jun. 30, 2022 USD ($) Plant
Federal Coal Ash Regulation
Site Contingency [Line Items]
Number of sites where regulated ash units will still be in operation at a specified date	3
Number of impoundments where closure plans will be expedited	1
Estimated cost of closure of an impoundment	$ 4
Time period of existing ash pond closure completion in accordance with the CCR rule	5 years
Federal Clean Water Act Section 316 (b) | NSP Minnesota [Member]
Site Contingency [Line Items]
Minimum number of plants which could be required to make improvements to reduce entrainment | Plant	6
Federal Clean Water Act Section 316 (b) | Capital Addition Purchase Commitments
Site Contingency [Line Items]
Liability for estimated cost to comply with regulation	$ 36