Derivative Financial Instruments - Narrative (Details) $ in Millions		3 Months Ended			6 Months Ended			12 Months Ended
		Jun. 30, 2016 USD ($) GWh	Jun. 30, 2015 USD ($) GWh		Jun. 30, 2016 USD ($) GWh		Jun. 30, 2015 USD ($) GWh	Dec. 31, 2014 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Derivative [Line Items]
Income taxes		$ 102	$ 327		$ 285		$ 690
Derivative, Notional Amount		100			100				$ 600
Derivative, Loss on Derivative		3
Derivative Instruments, Loss Recognized in Other Comprehensive Income (Loss), Effective Portion		3
Hypothetical increase in interest rates associated with variable-rate debt					3
Ineffective portion recognized in income	[1]	4			6
Mark-to-market derivative liabilities (noncurrent liabilities)		442			442					$ 374
Derivative Liability, Current		152			152					205
Cash collateral posted		9			9
Letters of credit posted		35			35
Interest Rate Fair Value Hedge Asset at Fair Value		39			39
Debt Instrument, Face Amount			750				750
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes		(31)	$ 181		120		$ 407
Mark-to-market derivative liabilities (noncurrent liabilities)		237			237					150
Derivative Liability, Current		134			134					182
Cash collateral received not offset against net derivative positions		10			10					3
Cash collateral posted		548			548					1,267
Letters of credit held		46			46					78
Letters of credit posted		441			441					497
Cash collateral held		14			14					21
Incremental collateral for loss of investment grade credit rating		1,800			1,800					2,000
Interest Rate Fair Value Hedge Asset at Fair Value		$ (7)			$ (7)
Derivative, Nonmonetary Notional Amount, Energy Measure | GWh		1,289	1,657		2,509		3,465
Debt Instrument, Face Amount		$ 10			$ 10
Commonwealth Edison Co [Member]
Derivative [Line Items]
Income taxes		91	$ 68		168		$ 127
Mark-to-market derivative liabilities (noncurrent liabilities)		203			203					224
Derivative Liability, Current		18			18					23
Cash collateral held		19			19
Incremental collateral for loss of investment grade credit rating		3			3
Credit Exposure Under Off System Sales		1			1
PECO Energy Co [Member]
Derivative [Line Items]
Income taxes		23	27		$ 67		85
Estimated percentage of natural gas purchases hedged					30.00%
Incremental collateral for loss of investment grade credit rating		26			$ 26
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Income taxes		6	32		73		105
Incremental collateral for loss of investment grade credit rating		31			31
Credit Exposure Under Off System Sales		1			1
Delmarva Power and Light Company [Member]
Derivative [Line Items]
Income taxes		8	5		(1)		26
Incremental collateral for loss of investment grade credit rating		9			$ 9
Minimum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months					97.00%
Expected Generation Hedged In Year Two					78.00%
Expected generation hedged in year three					47.00%
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					100.00%
Expected Generation Hedged In Year Two					81.00%
Expected generation hedged in year three					50.00%
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 [Line Items]
Derivative, Notional Amount		800			$ 800
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Liability, Current		4			4
Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative, Notional Amount		100			100
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount of Pre-issuance Interest Rate Cash Flow Hedge Derivatives		764			764
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Notional Amount of Pre-issuance Interest Rate Cash Flow Hedge Derivatives		674			674
Designated as Hedging Instrument [Member] | Commonwealth Edison Co [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	[2]	(221)			(221)					(247)
Mark-to-market derivative liabilities (noncurrent liabilities)		(203)			(203)					224
Derivative Liability, Current		(18)			(18)					23
Designated as Hedging Instrument [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Derivative, Fair Value, Net		1			1					(2)
Mark-to-market derivative liabilities (noncurrent liabilities)		0			0					0
Derivative Liability, Current		0			0					(2)
Foreign Exchange Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Notional Amount		100			100
Energy Related Derivative [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Brokered Natural Gas Margin Revenue					3
Derivative [Member]
Derivative [Line Items]
Derivative, Fair Value, Net		673			673					1,506
Mark-to-market derivative liabilities (noncurrent liabilities)		426			426					366
Derivative Liability, Current		143			143					197
Derivative [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	[3]	894			894					1,753
Mark-to-market derivative liabilities (noncurrent liabilities)	[3]	223			223					142
Derivative Liability, Current	[3]	125			125					174
Derivative [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Derivative, Fair Value, Net		0			0					0
Mark-to-market derivative liabilities (noncurrent liabilities)	[4]	0			0					0
Derivative Liability, Current	[4]	0			0					0
Fair Value Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		800			800					$ 800
Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments					47			$ 25
Cash Flow Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		90			90
Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments					1
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Increase In Notional Amount Of Derivative Instruments					177
Other Solar Projects [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Notional amounts on forward starting interest rate swaps		25			25
Other Solar Projects [Member] | Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Notional amounts on forward starting interest rate swaps		24			24
PHI Merger [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount			2,400				2,400
PHI Merger [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net							64
ExGen Texas Power [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		497			497
ExGen Texas Power [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities (noncurrent liabilities)		18			18
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	[5]		0		2		(10)
Cash Flow Hedge Gain Loss Reclassified To Pretax Net Income From Accumulated Other Comprehensive Income							2
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			$ 0	[5]	2	[5]	$ 0
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Income taxes	[5]				(2)
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		26			26
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility		40			40
Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility		36			36
Potomac Electric Power Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		50			50
Delmarva Power and Light Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		15			15
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		$ 8			$ 8

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

[2] .

[3] .

[4] Current and noncurrent assets are shown net of collateral of $352 million and $180 million, respectively, and current and noncurrent liabilities are shown net of collateral of $480 million and $222 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $1,234 million at December 31, 2015.

[5] Amounts in parenthesis represent a decrease in net income.