Pension, OPEB and Savings Plans (Estimated Future Benefit Payments) (Details) $ in Millions	Dec. 31, 2019 USD ($)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	$ 382
Payments Expected Year Two	354
Payments Expected Year Three	367
Payments Expected Year Four	378
Payments Expected Year Five	389
Payments Expected Thereafter	2,074
Total Estimated Future Benefit Payments	3,944
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	90
Payments Expected Year Two	85
Payments Expected Year Three	86
Payments Expected Year Four	86
Payments Expected Year Five	86
Payments Expected Thereafter	409
Total Estimated Future Benefit Payments	842
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	6
Payments Expected Year Two	8
Payments Expected Year Three	10
Payments Expected Year Four	12
Payments Expected Year Five	14
Payments Expected Thereafter	109
Total Estimated Future Benefit Payments	159
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	7
Payments Expected Year Two	9
Payments Expected Year Three	11
Payments Expected Year Four	13
Payments Expected Year Five	15
Payments Expected Thereafter	104
Total Estimated Future Benefit Payments	$ 159