Commitments and Contingencies - MEC - Transmission Rates (Details) - MEC $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)
Unfavorable regulatory action
Loss Contingencies [Line Items]
Loss contingency accrual	$ 8
Transmission
Loss Contingencies [Line Items]
Approved return on equity adder	0.50%
Transmission | Prior to September 2016
Loss Contingencies [Line Items]
Approved return on equity	12.38%
Transmission | November 2013 to February 2015
Loss Contingencies [Line Items]
Approved return on equity	10.32%
Intervenor proposed return on equity	9.15%
Transmission | February 2015 through May 2016
Loss Contingencies [Line Items]
Intervenor proposed return on equity	8.67%
Transmission | Nov 2019 Order For Nov 2013 to Feb 2015 and Sept 2016 Forward
Loss Contingencies [Line Items]
Approved return on equity	9.88%
Approved return on equity plus adder	10.38%
Transmission | May 2020 Order For Nov 2013 to Feb 2015 and Sept 2016 to May 2020
Loss Contingencies [Line Items]
Approved return on equity	10.02%
Approved return on equity plus adder	10.52%