Pension, OPEB and Savings Plans (Estimated Future Benefit Payments) (Details) $ in Millions	Dec. 31, 2016 USD ($)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	$ 310
Payments Expected Year Two	307
Payments Expected Year Three	319
Payments Expected Year Four	331
Payments Expected Year Five	343
Payments Expected Thereafter	1,887
Total Estimated Future Benefit Payments	3,497
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	82
Payments Expected Year Two	86
Payments Expected Year Three	90
Payments Expected Year Four	94
Payments Expected Year Five	99
Payments Expected Thereafter	534
Total Estimated Future Benefit Payments	985
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	2
Payments Expected Year Two	3
Payments Expected Year Three	5
Payments Expected Year Four	7
Payments Expected Year Five	8
Payments Expected Thereafter	76
Total Estimated Future Benefit Payments	101
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Payments Expected Next Twelve Months	4
Payments Expected Year Two	6
Payments Expected Year Three	9
Payments Expected Year Four	11
Payments Expected Year Five	13
Payments Expected Thereafter	96
Total Estimated Future Benefit Payments	$ 139