Regulatory and Rate Matters - Application For a New 345 KV Transmission Line (Details) $ in Millions	Aug. 10, 2018 USD ($) kv MW	Mar. 21, 2018 MW
KV Transmission Line
Public Utilities, General Disclosures [Line Items]
Transmission line and associated facilities generation capacity (in kilovolts) | kv	345
Solar generation capacity (in megawatts) | MW	166
Estimated cost of project | $	$ 85.0
Facebook Data Center
Public Utilities, General Disclosures [Line Items]
Estimated cost of project | $	$ 39.0
Estimated cost of project, percentage	46.00%
Facebook Data Center | Avangrid Renewables, LLC
Public Utilities, General Disclosures [Line Items]
Solar generation capacity (in megawatts) | MW		166