Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Change in fair value of commodity positions	$ 49	$ (92)	$ (5)
Reclassification to realized at settlement	58	(2)	(1)
Net mark-to market gains (losses)	357	(693)	507
Operating Revenue [Member]
Derivative [Line Items]
Change in fair value of commodity positions	404	(607)	460
Reclassification to realized at settlement		8	53
Net mark-to market gains (losses)		(599)	513
Operating Revenue [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	0	0	7
Intersegment Eliminations [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in fair value of commodity positions	0	0	(6)
Reclassification to realized at settlement	0	0	13
Net mark-to market gains (losses)	0	0	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)	107	(94)	(6)
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	36	(100)	0
Reclassification to realized at settlement	64	0	0
Net mark-to market gains (losses)	100	(100)	0
Other Segments [Member] | Interest Rate Swap [Member] | Interest Expense [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	100	(100)	0
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Change in fair value of commodity positions	404	(607)	466
Reclassification to realized at settlement	(154)	8	40
Net mark-to market gains (losses)	250	(599)	506
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	13	8	(5)
Reclassification to realized at settlement	(6)	(2)	(1)
Net mark-to market gains (losses)	257	(593)	500
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in fair value of commodity positions	759	(413)	286
Reclassification to realized at settlement	(563)	231	(64)
Net mark-to market gains (losses)	196	(182)	222
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Change in fair value of commodity positions	(355)	(194)	180
Reclassification to realized at settlement	409	(223)	104
Net mark-to market gains (losses)	54	(417)	284
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Derivative [Line Items]
Change in fair value of commodity positions	13	10	(1)
Reclassification to realized at settlement	(6)	(2)	(1)
Net mark-to market gains (losses)	203	(174)	220
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)	54	(417)	284
Exelon Generation Co L L C [Member] | Interest Expense [Member]
Derivative [Line Items]
Change in fair value of commodity positions	0	(2)	(4)
Reclassification to realized at settlement	0	0	0
Net mark-to market gains (losses)	0	(2)	(4)
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Purchased Power [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	7	6	(6)
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Operating Revenue [Member]
Derivative [Line Items]
Net mark-to market gains (losses)	7	8	(2)
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)	$ 0	$ (2)	$ (4)