Pension, OPEB and Savings Plans (Estimated Future Benefit Payments) (Details) $ in Millions	Dec. 31, 2018 USD ($)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	$ 345
Payments Expected Year Two	341
Payments Expected Year Three	352
Payments Expected Year Four	364
Payments Expected Year Five	373
Payments Expected Thereafter	2,004
Total Estimated Future Benefit Payments	3,779
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	91
Payments Expected Year Two	95
Payments Expected Year Three	87
Payments Expected Year Four	88
Payments Expected Year Five	89
Payments Expected Thereafter	428
Total Estimated Future Benefit Payments	878
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	4
Payments Expected Year Two	6
Payments Expected Year Three	7
Payments Expected Year Four	9
Payments Expected Year Five	11
Payments Expected Thereafter	91
Total Estimated Future Benefit Payments	128
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Other 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	99
Total Estimated Future Benefit Payments	$ 149