Derivative Financial Instruments - Summary of Economic Hedges (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative [Line Items]
Change in fair value	$ 200	$ 180	$ (493)	$ 217
Reclassification to realized at settlement	63	66	17	61
Net mark-to-market gains (losses)	263	246	(476)	278
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value	200	180	(493)	223
Reclassification to realized at settlement	63	66	17	48
Net mark-to-market gains (losses)	263	246	(476)	271
Other Segments [Member]
Derivative [Line Items]
Change in fair value	(6)		(12)	(3)
Reclassification to realized at settlement	(1)		(2)	0
Net mark-to-market gains (losses)	256	246	(490)	275
Purchased Power [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value	2	0	(4)	(3)
Reclassification to realized at settlement	(1)	0	(2)	0
Net mark-to-market gains (losses)	264		(482)	268
Operating Revenue One [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)				134
Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value	19	5	302	74
Reclassification to realized at settlement	(23)	25	(207)	63
Net mark-to-market gains (losses)	(4)	30	95	137
Interest Expense [Member]
Derivative [Line Items]
Change in fair value	0	0	0	0
Reclassification to realized at settlement	0	0	0	0
Net mark-to-market gains (losses)	0	0	0	0
Interest Expense [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)	0			0
Operating Revenue [Member]
Derivative [Line Items]
Change in fair value	0	0	0	(6)
Reclassification to realized at settlement	0	0	0	13
Net mark-to-market gains (losses)	0	0	0	7
Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value	181	175	(795)	149
Reclassification to realized at settlement	86	41	224	(15)
Net mark-to-market gains (losses)	267	216	(571)	134
Interest Rate Swap [Member] | Other Segments [Member]
Derivative [Line Items]
Change in fair value	(8)	0	(8)	0
Reclassification to realized at settlement	0	0	0	0
Net mark-to-market gains (losses)	(8)	0	(8)	0
Interest Expense [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value	(3)	0	(5)	(3)
Reclassification to realized at settlement	0	0	0	0
Net mark-to-market gains (losses)	(3)	0	(5)	(3)
Interest Expense [Member] | Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value				0
Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value	0	0	0	0
Reclassification to realized at settlement	0	0	0
Net mark-to-market gains (losses)	(4)	30	95	137
Operating Revenue [Member]
Derivative [Line Items]
Change in fair value	0	0	0	0
Reclassification to realized at settlement	0	0	0
Net mark-to-market gains (losses)	0		0	7
Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value	5	0	1	0
Reclassification to realized at settlement	(1)	0	(2)
Net mark-to-market gains (losses)	271		(572)
Operating Revenue [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in fair value				0
Operating Revenue [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value				0
Interest Rate Swap [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)		0
Interest Rate Swap [Member] | Other Segments [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)	(7)		(14)	(3)
Interest Rate Swap [Member] | Purchased Power [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)	1	0	(6)	(3)
Interest Rate Swap [Member] | Interest Rate Swap [Member] | Other Segments [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)	(8)	0	(8)	0
Interest Rate Swap [Member] | Interest Expense [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)	(3)	0	(5)	(3)
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	0	0
Interest Rate Swap [Member] | Operating Revenue [Member]
Derivative [Line Items]
Net mark-to-market gains (losses)	0	0	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)	$ 4		$ (1)	$ 0