Early Nuclear Plant Retirements Early Nuclear Plant Retirements (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	$ 1,183	$ 1,104
Property, plant and equipment, net	70,693	$ 57,439
Ginna [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	30
Nuclear Fuel, Net of Amortization	47
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	12
Asset Retirement Obligation	(659)
Property, plant and equipment, net	125
Three Mile Island [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	38
Nuclear Fuel, Net of Amortization	104
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	35
Asset Retirement Obligation	(485)
Property, plant and equipment, net	968
Nine Mile Point [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	69
Nuclear Fuel, Net of Amortization	235
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	70
Asset Retirement Obligation	(770)
Property, plant and equipment, net	$ 1,137