Investment in Constellation Energy Nuclear Group, LLC - Schedule of Assets and Liabilities of CENG (Details) - USD ($) $ in Millions	Mar. 23, 2016	Dec. 31, 2014	Apr. 01, 2014
Business Acquisition [Line Items]
Current assets	$ 1,441
Property, plant and equipment	11,088
Total assets	21,797
Current liabilities	2,752
Unamortized energy contract liabilities	1,515
Other liabilities	187
Total liabilities	14,655
Total net assets	$ 7,142
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Current assets		$ 390
Current liabilities		(196)
Unamortized energy contract liabilities		(110)
Other liabilities		$ 57
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
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