Commitments and Contingencies - Energy Purchase Commitments (Details $ in Millions	Sep. 30, 2022 USD ($) MW	Jul. 01, 2022 MW	Dec. 06, 2018 MW	Apr. 09, 2018 MW	Oct. 01, 2015 MW	Dec. 31, 2014 MW	May 01, 2012 MW	Jun. 30, 2010 MW
Legal Matters [Line Items]
LTCS Renewable Energy Contract, Three-State Procurement, Power				36.75
LTCS Renewable Energy Contract, Deepwater Agreement, Power								30
LTCS Renewable Energy Contract, Second Solicitation, Power							3.9
LTCS Renewable Energy Contract, Third Solicitation, Power					80
LTCS Renewable Energy Contract, Offshore Wind Energy Procurement, Power			408
Amount of MW Required to Meet LTCS Renewable Energy Contracting Capacity Requirement	3
LTCS Renewable Energy Contracting Capacity Requirement						90
Minimum [Member]
Legal Matters [Line Items]
ACES Renewable Energy Contracting Capacity Requirement		600
Maximum [Member]
Legal Matters [Line Items]
ACES Renewable Energy Contracting Capacity Requirement		1,000
Power Purchase | Rhode Island Energy
Legal Matters [Line Items]
Unrecorded Unconditional Purchase Obligation | $	$ 1,075
Unrecorded Unconditional Purchase Obligation, to be Paid, after Year Five | $	287
Unrecorded Unconditional Purchase Obligation, to be Paid, Years Two and Three | $	413
Unrecorded Unconditional Purchase Obligation, to be Paid, Years Four and Five | $	75
Unrecorded Unconditional Purchase Obligation, to be Paid, Remainder of Fiscal Year | $	$ 300