Derivative Financial Instruments (Interest Rate Risk) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended			3 Months Ended	9 Months Ended				3 Months Ended	9 Months Ended		3 Months Ended	9 Months Ended	12 Months Ended				9 Months Ended			3 Months Ended		9 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended				9 Months Ended	12 Months Ended		3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Fair Value Hedging [Member]	Sep. 30, 2013 Fair Value Hedging [Member]	Sep. 30, 2012 Fair Value Hedging [Member]	Sep. 30, 2013 Antelope Valle [Member] Interest Rate Cash Flow Hedge Derivatives Cash Flow Hedging [Member]	Sep. 30, 2013 Designated as Hedging Instrument [Member]	Sep. 30, 2013 Designated as Hedging Instrument [Member] Fair Value Hedging [Member]	Sep. 30, 2013 Designated as Hedging Instrument [Member] Fair Value Hedging [Member]	Sep. 30, 2012 Designated as Hedging Instrument [Member] Fair Value Hedging [Member]	Sep. 30, 2013 Designated as Hedging Instrument [Member] Interest Rate Swap Fair Value Hedging [Member]	Sep. 30, 2013 Designated as Hedging Instrument [Member] Interest Rate Swap Fair Value Hedging [Member]	Dec. 31, 2012 Designated as Hedging Instrument [Member] Interest Rate Swap Fair Value Hedging [Member]	Sep. 30, 2013 Designated as Hedging Instrument [Member] Other Solar Projects [Member] Interest Rate Cash Flow Hedge Derivatives Cash Flow Hedging [Member]	Sep. 30, 2013 Derivative [Member]	Sep. 30, 2013 Derivative [Member] Interest Rate Swap	Sep. 30, 2013 Exelon Generation Co L L C [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Fair Value Hedging [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Fair Value Hedging [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Fair Value Hedging [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Antelope Valle [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Antelope Valle [Member] Designated as Hedging Instrument [Member] Cash Flow Hedging [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member] Fair Value Hedging [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member] Fair Value Hedging [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member] Fair Value Hedging [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member] Fair Value Hedging [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member] Foreign Currency Fair Value Hedge Derivatives	Sep. 30, 2013 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member] Interest Rate Swap	Sep. 30, 2013 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member] Interest Rate Swap Fair Value Hedging [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member] Interest Rate Swap Fair Value Hedging [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member] Other Solar Projects [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member] Interest Expense [Member] Fair Value Hedging [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Designated as Hedging Instrument [Member] Interest Expense [Member] Fair Value Hedging [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Derivative [Member]	Dec. 31, 2012 Exelon Generation Co L L C [Member] Derivative [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Derivative [Member] Antelope Valle [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Derivative [Member] Interest Expense [Member] Antelope Valle [Member]	Sep. 30, 2013 Exelon Generation Co L L C [Member] Proprietary Trading [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member] Proprietary Trading [Member]		Sep. 30, 2013 Exelon Generation Co L L C [Member] Collateral And Netting [Member]		Dec. 31, 2012 Exelon Generation Co L L C [Member] Collateral And Netting [Member]		Sep. 30, 2013 Other Segment [Member] Designated as Hedging Instrument [Member]	Dec. 31, 2012 Other Segment [Member] Designated as Hedging Instrument [Member]
Cost Of Capital Strategies [Abstract]
Hypothetical increase in interest rates associated with variable-rate debt	0.50%
Pre-tax net income impact associated with a hypothetical 10% increase in interest rates - exclusive upper bound	$ 1
Derivative Interest Rate Risk [Abstract]
Mark-to-market derivative assets (current assets)	2		4															2		4																			3	3			18	[1]	20	[1]	(19)	[2]	19	[2]
Mark-to-market derivative assets (noncurrent assets)	46		59				2									23		33		46						27	38												5	8			17	[1]	32	[1]	(16)	[2]	32	[2]	13	13
Total mark-to-market derivative assets	48		63															35		50						27	38												8	11			35	[1]	52	[1]	(35)	[2]	51	[2]	13	13
Mark-to-market derivative liabilities (current liabilities)	(2)		(2)															(2)		(2)						(1)	(1)												(1)	(1)			(19)	[1]	(19)	[1]	19	[2]	(19)	[2]
Mark-to-market derivative liabilities (noncurrent liabilities)	(14)		(31)															(14)		(31)						(14)	(31)													0			(16)	[1]	(32)	[1]	16	[2]	(32)	[2]
Total mark-to-market derivative liabilities	(16)		(33)															(16)		(33)						(15)	(32)												(1)	(1)			(35)	[1]	(51)	[1]	35	[2]	(51)	[2]
Total mark-to-market derivative net assets (liabilities)	32		30															19		17						12	6												7	10			0	[1]	1	[1]	0	[2]			13	13
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Gain on swaps/borrowings						2			4	1
Loss on swaps/borrowings				(5)	(2)						(2)										(1)	(3)	(6)					(4)	(1)	(13)	(3)
Interest Rate Risk - Fair Value Hedges [Abstract]
Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments													40	49																				27	38
Interest rate swaps previously held by acquiree																																		550	550
Notional amount of interest rate swaps acquired from merger	150
Fair value of interest rate swaps acquired from merger	3
Interest Rate Risk - Cash Flow Hedges [Abstract]
Notional Amount of Pre-issuance Interest Rate Cash Flow Hedge Derivatives								213
Pre-tax gain/loss on interest rate cash flow hedges																																					(4)	(12)
DOE loan guarantee																		646
DOE interest rate swap																									485
Percentage of interest rate swap in relation to DOE guarantee																		75
Notional amount of interest rate swap DOE advance																		328
Percent of DOE loan advance offset																		75.00%
Notional amount of remaining cash flow hedges																		156
Notional amounts on forward starting interest rate swaps																								29												28
Mark-to-market derivative liabilities	218		281															112		232																					2	13
Unrealized Gain (Loss) on Derivatives	229	377																222	345
Derivative, Notional Amount												1,100	1,100	650			1,250															38	134
Deferred Gain on Derivatives															26
Increase In Notional Amount Of Derivative Instruments												$ 450

[1]                  Generation enters into interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions.  The characterization of the interest rate derivative contracts between the proprietary trading activity in the above table is driven by the corresponding characterization of the underlying commodity position that gives rise to the interest rate exposure.  Generation does not utilize interest rate derivatives with the objective of benefiting from shifts or changes in market interest rates.

[2] Represents the netting of fair value balances with the same counterparty and any associated cash collateral.