Early Nuclear Plant Retirements Early Nuclear Plant Retirements (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	$ 1,188	$ 1,104
Property, plant and equipment, net	71,214	$ 57,439
Ginna [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	31
Nuclear Fuel, Net of Amortization	41
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	13
Asset Retirement Obligation	(667)
Property, plant and equipment, net	124
Three Mile Island [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	39
Nuclear Fuel, Net of Amortization	93
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	38
Asset Retirement Obligation	(492)
Property, plant and equipment, net	956
Nine Mile Point [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	70
Nuclear Fuel, Net of Amortization	214
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	53
Asset Retirement Obligation	(780)
Property, plant and equipment, net	$ 1,151