Pension, OPEB and Savings Plans (Estimated Future Benefit Payments) (Details) $ in Millions	Dec. 31, 2020 USD ($)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	$ 389
Payments Expected Year Two	368
Payments Expected Year Three	381
Payments Expected Year Four	392
Payments Expected Year Five	401
Payments Expected Thereafter	2,119
Total Estimated Future Benefit Payments	4,050
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	83
Payments Expected Year Two	84
Payments Expected Year Three	84
Payments Expected Year Four	84
Payments Expected Year Five	83
Payments Expected Thereafter	388
Total Estimated Future Benefit Payments	806
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	8
Payments Expected Year Two	10
Payments Expected Year Three	12
Payments Expected Year Four	15
Payments Expected Year Five	17
Payments Expected Thereafter	123
Total Estimated Future Benefit Payments	185
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	9
Payments Expected Year Two	11
Payments Expected Year Three	13
Payments Expected Year Four	15
Payments Expected Year Five	17
Payments Expected Thereafter	111
Total Estimated Future Benefit Payments	$ 176