Investment in Constellation Energy Nuclear Group, LLC - Schedule of Assets and Liabilities of CENG (Details) $ in Millions	Mar. 31, 2016 USD ($)
Schedule of Equity Method Investments [Line Items]
Current assets	$ 2,107
Property, plant and equipment	11,071
Total assets	22,968
Current liabilities	3,425
Unamortized energy contract liabilities	1,550
Other liabilities	191
Total liabilities	15,826
Total net assets	$ 7,142