Implications of Potential Early Plant Retirements Implications of Potential Early Plant Retirement (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	$ 1,229	$ 1,104
Property, plant and equipment, net	69,406	$ 57,439
Quad Cities [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	47
Nuclear Fuel, Net of Amortization	213
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	28
Asset Retirement Obligation	(706)
Property, plant and equipment, net	1,014
Clinton [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	58
Nuclear Fuel, Net of Amortization	95
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	11
Asset Retirement Obligation	(407)
Property, plant and equipment, net	574
Ginna [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	30
Nuclear Fuel, Net of Amortization	54
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	11
Asset Retirement Obligation	(651)
Property, plant and equipment, net	127
Nuclear Plant [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	135
Nuclear Fuel, Net of Amortization	362
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	50
Asset Retirement Obligation	(1,764)
Property, plant and equipment, net	$ 1,715