Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Derivative [Line Items]
Change in fair value	$ 152	$ 85
Reclassification to realized at settlement	(44)	66
Net mark-to-market gains (losses)	108	151
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value	152	85
Reclassification to realized at settlement	(44)	66
Net mark-to-market gains (losses)	108	151
Other Segments [Member]
Derivative [Line Items]
Change in fair value	(3)	(65)
Reclassification to realized at settlement	(2)	(2)
Net mark-to-market gains (losses)	103	84
Purchased Power [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value	(3)	13
Reclassification to realized at settlement	(2)	(2)
Net mark-to-market gains (losses)	103	162
Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value	(127)	(79)
Reclassification to realized at settlement	167	87
Net mark-to-market gains (losses)	40	8
Interest Expense [Member]
Derivative [Line Items]
Change in fair value		0
Reclassification to realized at settlement		0
Net mark-to-market gains (losses)		0
Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value	279	164
Reclassification to realized at settlement	(211)	(21)
Net mark-to-market gains (losses)	68	143
Interest Rate Swap [Member] | Other Segments [Member]
Derivative [Line Items]
Change in fair value		(78)
Reclassification to realized at settlement		0
Net mark-to-market gains (losses)		(78)
Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value	0	0
Reclassification to realized at settlement	0	0
Net mark-to-market gains (losses)	40	8
Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value	(3)	13
Reclassification to realized at settlement	(2)	(2)
Net mark-to-market gains (losses)	63	154
Interest Rate Swap [Member] | Other Segments [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)	(5)	(67)
Interest Rate Swap [Member] | Purchased Power [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)	(5)	11
Interest Rate Swap [Member] | Interest Rate Swap [Member] | Other Segments [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)		(78)
Interest Rate Swap [Member] | Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)	0	0
Interest Rate Swap [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)	$ (5)	$ 11