Pension, OPEB and Savings Plans (Estimated Future Benefit Payments) (Details) $ in Millions	Dec. 31, 2015 USD ($)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2016	$ 285
2017	295
2018	305
2019	317
2020	329
2021-2025	1,818
Total Estimated Future Benefit Payments	3,349
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2016	81
2017	84
2018	87
2019	91
2020	95
2021-2025	518
Total Estimated Future Benefit Payments	956
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2016	1
2017	2
2018	3
2019	4
2020	6
2021-2025	60
Total Estimated Future Benefit Payments	76
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2016	3
2017	5
2018	7
2019	8
2020	10
2021-2025	80
Total Estimated Future Benefit Payments	$ 113