Pension And OPEB (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions			$ 15
Total Benefit Costs	$ 18	$ (5)	37	$ (11)
Postretirement Healthcare Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions			14
Total Benefit Costs	22	18	44	35
Long Island Electric Utility Servco LLC Pension and OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year			30
Total Benefit Costs	$ 7	$ 23	$ 13	$ 46