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Area of land held.

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The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

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Related Party Transactions - Additional Information (Details)		1 Months Ended	3 Months Ended
	Mar. 02, 2020 MW	May 31, 2018 MW	Mar. 31, 2020 USD ($) mi² MW	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Related Party Transaction [Line Items]
Proposed wind farm and electricity transmission project capacity (MW) \| MW	681
Portion of amount receivable from related parties					$ 1,000,000
Deposit balance			$ 0		150,000,000
Line of credit facility fee basis points			0.105%
Credit facility outstanding amount			$ 350,000,000		0
Affiliated Entity
Related Party Transaction [Line Items]
Impairments			$ 0
New York Transco
Related Party Transaction [Line Items]
New electric generation and transmission capacity (MW) \| MW			3,200
Amount of commitment funded to date			$ 600,000,000
Vineyard Wind
Related Party Transaction [Line Items]
New electric generation and transmission capacity (MW) \| MW		804
Leased area transmission capacity (MW) \| MW			3,000
Proposed wind farm and electricity transmission project capacity (MW) \| MW		800
Portion of amount receivable from related parties			$ 3,000,000		5,000,000
Iberdrola Solutions
Related Party Transaction [Line Items]
Portion of amount receivable from related parties					0
Iberdrola Financiacion, S.A.U
Related Party Transaction [Line Items]
Line of credit facility, maximum borrowing capacity			500,000,000
Credit facility outstanding amount			$ 0
Iberdrola, S.A. \| Siemens-Gamesa
Related Party Transaction [Line Items]
Business acquisition, percentage of voting interests acquired			8.10%
Related party transaction, amount			$ 11,000,000	$ 18,000,000
Networks \| New York Transco
Related Party Transaction [Line Items]
Business combination, equity interest percentage			20.00%
Amount of commitment funded to date			$ 120,000,000
Portion of amount receivable from related parties			$ 0		1,000,000
Renewables \| Vineyard Wind
Related Party Transaction [Line Items]
Business combination, equity interest percentage			50.00%
Amount of commitment funded to date			$ 137,000,000
Square mileage of land containing development rights \| mi²			260
Portion of amount receivable from related parties			$ 3,000,000		$ 5,000,000
Renewables \| Second Offshore Development Project
Related Party Transaction [Line Items]
Amount of commitment funded to date			$ 106,000,000