Derivative Financial Instruments - Narrative (Details) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) MWh		Jun. 30, 2014 USD ($) MWh	Dec. 31, 2014 USD ($)
Derivative [Line Items]
Income taxes		$ 327	$ 277	$ 690		$ 224
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax			63	$ 2		102
Hypothetical Increase In Interest Rates				0.50%
Mark-to-market derivative assets (noncurrent assets)		811		$ 811			$ 773
Hypothetical increase in interest rates associated with variable-rate debt				2
Ineffective portion recognized in income		4	5	8	[1]	8
Mark-to-market derivative liabilities (noncurrent liabilities)		595		595			403
Cash collateral held		30		30
Letters of credit collateral posted		18		18
Interest Rate Fair Value Hedge Asset at Fair Value		31		31
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount of Pre-issuance Interest Rate Cash Flow Hedge Derivatives		754		754
Energy Supply Procurement [Member]
Derivative [Line Items]
Derivative Asset, Fair Value of Collateral		2		2
ReNewAble Energy Contract [Member]
Derivative [Line Items]
Derivative Asset, Fair Value of Collateral		19		19
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes		181	199	$ 407		$ (1)
Proprietary trading activities volume | MWh				3,006,000		8,129,000
Mark-to-market derivative assets (noncurrent assets)		790		$ 790			771
Mark-to-market derivative liabilities (noncurrent liabilities)		392		392			105
Cash collateral received not offset against net derivative positions		2		2			8
Credit exposure under natural gas supply and management agreements		2,244		2,244
Cash collateral posted		1,020		1,020			1,497
Letters of credit collateral posted		511		511			672
Cash collateral held		39		39			77
Letters of credit collateral posted		23		23			24
Incremental collateral for loss of investment grade credit rating		2,200		2,200			2,400
Interest Rate Fair Value Hedge Asset at Fair Value		10		10
Commonwealth Edison Co [Member]
Derivative [Line Items]
Income taxes		68	72	127		$ 137
Mark-to-market derivative liabilities (noncurrent liabilities)		203		203			187
PECO Energy Co [Member]
Derivative [Line Items]
Income taxes		27	23	$ 85		57
Estimated percentage of natural gas purchases hedged				30.00%
Total		3		$ 3
Incremental collateral for loss of investment grade credit rating		20		20
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Income taxes		32	14	105		72
Total		1		1
Incremental collateral for loss of investment grade credit rating		34		$ 34
Minimum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months				98.00%
Expected Generation Hedged In Year Two				77.00%
Expected generation hedged in year three				46.00%
Minimum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged				10.00%
Maximum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months				101.00%
Expected Generation Hedged In Year Two				80.00%
Expected generation hedged in year three				49.00%
Maximum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged				20.00%
Interest Rate Swap [Member] | Derivative [Member]
Derivative [Line Items]
Derivative, Notional Amount		800		$ 800
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities (noncurrent liabilities)		2		2
Foreign Exchange Contract [Member] | Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		146		146
Fair Value Hedging [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		800		800			1,450
Derivative, Gain (Loss) on Derivative, Net		(11)	3
Mark-to-market derivative assets (noncurrent assets)		20		20			29
Fair Value Hedging [Member] | Interest Rate Swap [Member] | Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount							550
Derivative, Gain (Loss) on Derivative, Net	[1]	0	(3)
Mark-to-market derivative assets (noncurrent assets)							7
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount of Pre-issuance Interest Rate Cash Flow Hedge Derivatives							$ 400
Other Solar Projects [Member] | Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional amounts on forward starting interest rate swaps		25		25
Mark-to-market derivative liabilities (noncurrent liabilities)		2		2
Other Solar Projects [Member] | Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		26		26
PHI Merger [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net				64
PHI Merger [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		2,400		2,400
ExGen Texas Power [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		502		502
ExGen Texas Power [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities (noncurrent liabilities)		10		10
ExGen Texas Power [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		201		201
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax				26
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Income taxes	[2]	0	25	(10)		40
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes	[2]	0	$ 25	0		$ 40
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		36		36
PECO Energy Co Affiliate [Member] | PECO Energy Co [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility		35		35
Baltimore Gas And Electric Company Affiliate [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility		$ 31		$ 31

[1] For the three and six months ended June 30, 2015, the loss on Generation swaps included $0 million and $1 million realized in earnings, respectively, with an immaterial amount excluded from hedge effectiveness testing. For the three and six months ended June 30, 2014, the loss on Generation swaps included $4 million and $8 million realized in earnings, respectively, with an immaterial amount excluded from hedge effectiveness testing.

[2] All amounts are net of tax. Amounts in parentheses represent a decrease in net income.