Subsequent Event (Details) - Forecast $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2021 USD ($) $ / shares
Merger Agreement
Subsequent Event [Line Items]
Business combination, cash right per common share (in dollars per share) | $ / shares	$ 50.30
Out-of-pocket fees and expenses reimbursement	$ 10.0
PNMR | Merger Agreement
Subsequent Event [Line Items]
Termination fees	130.0
Avangrid | Merger Agreement
Subsequent Event [Line Items]
Termination fees	$ 184.0
Avangrid | Iberdrola, S.A.
Subsequent Event [Line Items]
Noncontrolling interest, ownership percentage by parent	81.50%