Commitments and Contingencies - Transmission Rates (Details) - MEC - Transmission $ in Millions	6 Months Ended
	Jun. 30, 2022 USD ($)
Loss Contingencies [Line Items]
Public utilities, approved return on equity adder	0.50%
Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Accrued liability for estimated transmission billings refunds	$ 8
Prior to September 2016
Loss Contingencies [Line Items]
Public utilities, approved return on equity	12.38%
November 2013 to February 2015
Loss Contingencies [Line Items]
Public utilities, approved return on equity	10.32%
Public utilities, proposed return on equity	9.15%
February 2015 through May 2016
Loss Contingencies [Line Items]
Public utilities, proposed return on equity	8.67%
Nov 2019 Order For Nov 2013 to Feb 2015 and Sept 2016 Forward
Loss Contingencies [Line Items]
Public utilities, approved return on equity	9.88%
Public utilities, approved return on equity plus adder	10.38%
May 2020 Order For Nov 2013 to Feb 2015 and Sept 2016 Forward
Loss Contingencies [Line Items]
Public utilities, approved return on equity	10.02%
Public utilities, approved return on equity plus adder	10.52%