Variable Interest Entities (VIEs) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Variable Interest Entity [Line Items]
Operating Revenues	$ 1,874	$ 2,050	$ 4,763	$ 4,831
Operation and Maintenance	783	733	1,561	1,487
Long Island ServCo [Member]
Variable Interest Entity [Line Items]
Operating Revenues	129	125	252	252
Operation and Maintenance	129	$ 125	252	$ 252
Ocean Wind JV Holdco
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 91		$ 91