Variable Interest Entities (VIEs) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Variable Interest Entity [Line Items]
Operating Revenues	$ 1,903	$ 2,370	$ 6,666	$ 7,201
Operation and Maintenance	807	767	2,368	2,254
Long Island ServCo [Member]
Variable Interest Entity [Line Items]
Operating Revenues	142	145	394	397
Operation and Maintenance	142	$ 145	394	$ 397
Ocean Wind JV Holdco
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 98		$ 98