Derivative Financial Instruments - Summary of Economic Hedges (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Change in fair value of commodity positions	$ (92)	$ (5)	$ 6
Reclassification to realized at settlement	(2)	(1)	(3)
Net mark-to market gains (losses)	(693)	507	533
Operating Revenue [Member]
Derivative [Line Items]
Change in fair value of commodity positions	(607)	460	(241)
Reclassification to realized at settlement		53	771
Net mark-to market gains (losses)		513	530
Operating Revenue [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	0	7	7
Intersegment Eliminations [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in fair value of commodity positions	0	(6)	(94)
Reclassification to realized at settlement	0	13	101
Net mark-to market gains (losses)	0	7	7
Intersegment Eliminations [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in fair value of commodity positions	0	0	0
Reclassification to realized at settlement	0	0	0
Interest Rate Swap [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	(94)	(6)	3
Interest Rate Swap [Member] | Intersegment Eliminations [Member] | Operating Revenue [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	0	0	0
Other Segments [Member] | Interest Expense [Member]
Derivative [Line Items]
Change in fair value of commodity positions	0	0	0
Reclassification to realized at settlement	0	0	0
Net mark-to market gains (losses)	0	0	0
Other Segments [Member] | Interest Expense [Member]
Derivative [Line Items]
Change in fair value of commodity positions	(100)	0	0
Reclassification to realized at settlement	0	0	0
Net mark-to market gains (losses)	(100)	0	0
Other Segments [Member] | Interest Rate Swap [Member] | Interest Expense [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	(100)	0	0
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value of commodity positions	(607)	466	(147)
Reclassification to realized at settlement	8	40	670
Net mark-to market gains (losses)	(599)	506	523
Exelon Generation Co L L C [Member] | Interest Expense [Member]
Derivative [Line Items]
Change in fair value of commodity positions	0	0	0
Reclassification to realized at settlement	0	0	0
Net mark-to market gains (losses)	0	0	0
Exelon Generation Co L L C [Member] | Purchased Power [Member]
Derivative [Line Items]
Change in fair value of commodity positions	8	(5)	6
Reclassification to realized at settlement	(2)	(1)	(3)
Net mark-to market gains (losses)	(593)	500	526
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in fair value of commodity positions	(413)	286	(362)
Reclassification to realized at settlement	231	(64)	432
Net mark-to market gains (losses)	(182)	222	70
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Change in fair value of commodity positions	(194)	180	215
Reclassification to realized at settlement	(223)	104	238
Net mark-to market gains (losses)	(417)	284	453
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in fair value of commodity positions	10	(1)	0
Reclassification to realized at settlement	(2)	(1)	(3)
Net mark-to market gains (losses)	(174)	220	67
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Change in fair value of commodity positions	0	0	0
Reclassification to realized at settlement	0	0	0
Net mark-to market gains (losses)	(417)	284	453
Exelon Generation Co L L C [Member] | Interest Expense [Member]
Derivative [Line Items]
Change in fair value of commodity positions	(2)	(4)	6
Reclassification to realized at settlement	0	0	0
Net mark-to market gains (losses)	(2)	(4)	6
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Purchased Power [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	6	(6)	3
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Operating Revenue [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	8	(2)	(3)
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	0	0	0
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Interest Expense [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	$ (2)	$ (4)	$ 6