Derivative Financial Instruments (Interest Rate Risk) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Mar. 12, 2012
Cost Of Capital Strategies [Abstract]
Hypothetical increase in interest rates associated with variable-rate debt	50.00%
Pre-tax net income impact associated with a hypothetical 10% increase in interest rates - exclusive upper bound	$ 2.00
Derivative Interest Rate Risk [Abstract]
Mark-to-market derivative assets (current assets)	4.00
Mark-to-market derivative assets (noncurrent assets)	59.00
Total mark-to-market derivative assets	63.00
Mark-to-market derivative liabilities (current liabilities)	(2.00)
Mark-to-market derivative liabilities (noncurrent liabilities)	(31.00)
Total mark-to-market derivative liabilities	(33.00)
Total mark-to-market derivative net assets (liabilities)	30.00
Interest Rate Risk - Fair Value Hedges [Abstract]
Notional amounts of fair value hedges outstanding related to interest rate swaps	650.00	100.00
Interest rate swaps previously held by acquiree				550.00
Fair value of interest rate swaps from merger acquiree	150.00			44.00
Interest Rate Risk - Cash Flow Hedges [Abstract]
Mark-to-market derivative liabilities	281.00	126.00
Unrealized Gain (Loss) on Derivatives	604.00	(291.00)	88.00
Interest Expense [Member]
Derivative Instruments Gain Loss Recognized In Income Net [Abstract]
Loss on swaps/borrowings	(6.00)	(1.00)	(4.00)
Interest Rate Risk - Cash Flow Hedges [Abstract]
Unrealized Gain (Loss) on Derivatives	5.00
Designated as Hedging Instrument [Member]
Interest Rate Risk - Fair Value Hedges [Abstract]
Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments	49.00	15.00
Interest Rate Risk - Cash Flow Hedges [Abstract]
Notional amount of interest rate cash flow hedge derivatives	800.00
Notional Amount of Pre-issuance Interest Rate Cash Flow Hedge Derivatives	452.00
Notional amounts on forward starting interest rate swaps	75.00
Designated as Hedging Instrument [Member] | Interest Expense [Member]
Derivative Instruments Gain Loss Recognized In Income Net [Abstract]
Gain on swaps/borrowings		1.00	4.00
Interest Rate Risk - Fair Value Hedges [Abstract]
Notional amounts of fair value hedges outstanding related to interest rate swaps	(6.00)
Interest Rate Risk - Cash Flow Hedges [Abstract]
Pre-tax gain/loss on interest rate cash flow hedges	(12.00)
Derivative [Member]
Derivative Interest Rate Risk [Abstract]
Mark-to-market derivative assets (noncurrent assets)	1.00
Exelon Generation Co L L C [Member]
Cost Of Capital Strategies [Abstract]
Pre-tax net income impact associated with a hypothetical 10% increase in interest rates - exclusive upper bound	2.00
Derivative Interest Rate Risk [Abstract]
Mark-to-market derivative assets (current assets)	4.00
Mark-to-market derivative assets (noncurrent assets)	46.00
Total mark-to-market derivative assets	50.00
Mark-to-market derivative liabilities (current liabilities)	(2.00)
Mark-to-market derivative liabilities (noncurrent liabilities)	(31.00)
Total mark-to-market derivative liabilities	(33.00)
Total mark-to-market derivative net assets (liabilities)	17.00
Interest Rate Risk - Cash Flow Hedges [Abstract]
DOE loan guarantee	646.00
DOE interest rate swap	485.00
Mark-to-market derivative liabilities	232.00	29.00
Unrealized Gain (Loss) on Derivatives	611.00	(291.00)	88.00
Exelon Generation Co L L C [Member] | Antelope Valley Project [Member]
Interest Rate Risk - Cash Flow Hedges [Abstract]
Notional amount of interest rate cash flow hedge derivatives	485.00
Percentage of interest rate swap in relation to DOE guarantee	75
Notional amount of interest rate swap DOE advance	165.00
Percent of DOE loan advance offset	75.00%
Notional amount of remaining cash flow hedges	320.00
Mark-to-market derivative liabilities	28.00
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative Interest Rate Risk [Abstract]
Mark-to-market derivative assets (noncurrent assets)	38.00
Total mark-to-market derivative assets	38.00
Mark-to-market derivative liabilities (current liabilities)	(1.00)
Mark-to-market derivative liabilities (noncurrent liabilities)	(31.00)
Total mark-to-market derivative liabilities	(32.00)
Total mark-to-market derivative net assets (liabilities)	6.00
Interest Rate Risk - Fair Value Hedges [Abstract]
Notional amount of interest rate swaps acquired from merger	29.00
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member] | Other Solar Projects [Member]
Interest Rate Risk - Cash Flow Hedges [Abstract]
Notional amounts on forward starting interest rate swaps	29.00
Exelon Generation Co L L C [Member] | Derivative [Member]
Derivative Interest Rate Risk [Abstract]
Mark-to-market derivative assets (current assets)	3.00
Mark-to-market derivative assets (noncurrent assets)	8.00
Total mark-to-market derivative assets	11.00
Mark-to-market derivative liabilities (current liabilities)	(1.00)
Total mark-to-market derivative liabilities	(1.00)
Total mark-to-market derivative net assets (liabilities)	10.00
Exelon Generation Co L L C [Member] | Proprietary Trading [Member]
Derivative Interest Rate Risk [Abstract]
Mark-to-market derivative assets (current assets)	20.00
Mark-to-market derivative assets (noncurrent assets)	32.00
Total mark-to-market derivative assets	52.00
Mark-to-market derivative liabilities (current liabilities)	(19.00)
Mark-to-market derivative liabilities (noncurrent liabilities)	(32.00)
Total mark-to-market derivative liabilities	(51.00)
Total mark-to-market derivative net assets (liabilities)	1.00
Exelon Generation Co L L C [Member] | Collateral And Netting [Member]
Derivative Interest Rate Risk [Abstract]
Mark-to-market derivative assets (current assets)	(19.00)
Mark-to-market derivative assets (noncurrent assets)	(32.00)
Total mark-to-market derivative assets	(51.00)
Mark-to-market derivative liabilities (current liabilities)	19.00
Mark-to-market derivative liabilities (noncurrent liabilities)	32.00
Total mark-to-market derivative liabilities	51.00
Total mark-to-market derivative net assets (liabilities)	0
Other Segment [Member] | Designated as Hedging Instrument [Member]
Derivative Interest Rate Risk [Abstract]
Mark-to-market derivative assets (noncurrent assets)	13.00
Total mark-to-market derivative assets	13.00
Mark-to-market derivative liabilities (noncurrent liabilities)	(4.00)
Total mark-to-market derivative net assets (liabilities)	$ 13.00