Early Nuclear Plant Retirements Early Nuclear Plant Retirements (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	$ 1,312	$ 1,274
Property, plant and equipment, net	72,630	$ 71,555
Three Mile Island [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross	40
Nuclear Fuel, Net of Amortization	72
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	40
Asset Retirement Obligation	(572)
Property, plant and equipment, net	$ 1,000