Commitments and Contingencies - Energy Purchase Commitments (Details $ in Millions	Jul. 01, 2022 MW	Jun. 30, 2022 USD ($) MW	May 01, 2020 MW	Dec. 06, 2018 MW	Apr. 09, 2018 MW	Oct. 01, 2015 MW	Dec. 31, 2014 MW	Oct. 01, 2013 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								48
LTCS Renewable Energy Contract, Fourth Solicitation, Power						80
LTCS Renewable Energy Contract, Offshore Wind Energy Procurement, Power				408
LTCS Renewable Energy Contract, Fifth Solicitation, Power			49.5
Amount of MW Required to Meet LTCS Renewable Energy Contracting Capacity Requirement		3
LTCS Renewable Energy Contracting Capacity Requirement							90
Subsequent Event [Member] | Minimum [Member]
Legal Matters [Line Items]
ACES Renewable Energy Contracting Capacity Requirement	600
Subsequent Event [Member] | 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 | $		$ 809
Unrecorded Unconditional Purchase Obligation, to be Paid, after Year Five | $		312
Unrecorded Unconditional Purchase Obligation, to be Paid, Years Two and Three | $		216
Unrecorded Unconditional Purchase Obligation, to be Paid, Years Four and Five | $		81
Unrecorded Unconditional Purchase Obligation, to be Paid, Remainder of Fiscal Year | $		$ 200