Pension And OPEB (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	$ 30
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Benefit Costs	(29)	$ (20)
Postretirement Healthcare Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Benefit Costs	(31)	(24)
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Benefit Costs	8	9
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Postretirement Healthcare Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Benefit Costs	$ 2	$ 3