Pension, OPEB and Savings Plans (Assumptions Used To Determine The Benefit Obligations And Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	3.73%	4.29%	4.54%
Expected Return on Plan Assets	7.80%	8.00%	8.00%
Rate of Compensation Increase	3.90%	3.61%	3.61%
Service Cost Interest Rate	4.53%	4.81%	4.20%
Interest Cost Interest Rate	3.63%	3.75%	4.20%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.61%	3.61%	3.61%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.29%	4.54%	4.20%
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	3.76%	4.37%	4.58%
Expected Return on Plan Assets	7.80%	8.00%	8.00%
Rate of Compensation Increase	3.90%	3.61%	3.61%
Service Cost Interest Rate	4.64%	4.87%	4.21%
Interest Cost Interest Rate	3.69%	3.76%	4.21%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.61%	3.61%	3.61%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.37%	4.58%	4.21%
Immediate Rate	7.93%	7.55%	7.75%
Ultimate Rate	4.75%	4.75%	4.75%
Year Ultimate Rate Reached	2026	2025	2025
Total of Service Cost and Interest Cost effect of 1 percent increase	$ 13	$ 11	$ 12
Postretirement Benefit Obligation effect of 1 percent increase	240	191	194
Total of Service Cost and Interest Cost effect of 1 percent decrease	(10)	(9)	(10)
Postretirement Benefit Obligation effect of 1 percent decrease	$ (198)	$ (160)	$ (160)
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	3.90%	4.61%	4.92%
Expected Return on Plan Assets	7.60%
Rate of Compensation Increase	3.25%	3.25%	3.25%
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	3.96%	4.71%	4.97%
Rate of Compensation Increase	3.25%	3.25%	3.25%
Immediate Rate	7.69%	7.55%	7.55%
Ultimate Rate	4.75%	4.75%	4.75%
Year Ultimate Rate Reached	2026	2025	2025
Postretirement Benefit Obligation effect of 1 percent increase	$ 131	$ 97	$ 75
Postretirement Benefit Obligation effect of 1 percent decrease	$ (99)	$ (75)	$ (60)