Investment in Constellation Energy Nuclear Group, LLC - Schedule of Assets and Liabilities of CENG (Details) - Exelon Generation Co L L C [Member] - Constellation Energy Nuclear Group [Member] $ in Millions	Apr. 01, 2014 USD ($)
Business Acquisition [Line Items]
Current assets	$ 499
Nuclear decommissioning trust fund	1,955
Property, plant and equipment	3,073
Nuclear fuel	482
Other assets	10
Total assets	6,019
Current liabilities	237
Asset retirement obligation	1,816
Pension and other employee benefit obligations	281
Unamortized energy contract liabilities	171
Other liabilities	114
Total liabilities	2,619
Total net assets	$ 3,400