Pension, OPEB and Savings Plans (Schedule Of Percentage Of Fair Value Of Total Plan Assets) (Details)	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocation, percent	100.00%	100.00%
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocation, percent	69.00%	70.00%
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocation, percent	29.00%	28.00%
Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocation, percent	2.00%	2.00%
Long Island Electric Utility Servco LLC Pension and OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocation, percent	100.00%	100.00%
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocation, percent	72.00%	71.00%
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual plan asset allocation, percent	28.00%	29.00%