Derivative Financial Instruments - Narrative (Details) $ in Millions		3 Months Ended					9 Months Ended			12 Months Ended
		Sep. 30, 2016 USD ($) GWh	Jun. 30, 2016 USD ($)	Sep. 30, 2015 USD ($) GWh		Jun. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) GWh		Sep. 30, 2015 USD ($) GWh	Dec. 31, 2015 USD ($)	Mar. 31, 2016 USD ($)
Derivative [Line Items]
Income taxes		$ 340		$ 115			$ 625		$ 805
Derivative, Notional Amount			$ 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							5
Ineffective portion recognized in income	[1]	6					12
Mark-to-market derivative liabilities (noncurrent liabilities)		422					422			$ 374
Derivative Liability, Current		222					222			205
Cash collateral posted		10					10
Letters of credit posted		22					22
Interest Rate Fair Value Hedge Asset at Fair Value		35					35
Debt Instrument, Face Amount				750					750
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes		173		$ (36)			293		$ 371
Mark-to-market derivative liabilities (noncurrent liabilities)		197					197			150
Derivative Liability, Current		203					203			182
Cash collateral received not offset against net derivative positions		(5)					(5)			3
Cash collateral posted		501					501			1,267
Letters of credit held		22					22			78
Letters of credit posted		420					420			497
Cash collateral held		18					18			21
Incremental collateral for loss of investment grade credit rating		1,900					1,900			2,000
Interest Rate Fair Value Hedge Asset at Fair Value		$ (4)					$ (4)
Derivative, Nonmonetary Notional Amount, Energy Measure | GWh		1,506		1,913			4,015		5,378
Commonwealth Edison Company [Member]
Derivative [Line Items]
Cash collateral held		$ 3					$ 3
Commonwealth Edison Co [Member]
Derivative [Line Items]
Income taxes		75		$ 99			244		$ 226
Mark-to-market derivative liabilities (noncurrent liabilities)		225					225			224
Derivative Liability, Current		19					19			23
Cash collateral held		19					19
Incremental collateral for loss of investment grade credit rating		17					17
Credit Exposure Under Off System Sales		1					1
PECO Energy Co [Member]
Derivative [Line Items]
Income taxes		54		37			$ 121		122
Estimated percentage of natural gas purchases hedged							25.00%
Incremental collateral for loss of investment grade credit rating		25					$ 25
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Income taxes		36		35			109		141
Incremental collateral for loss of investment grade credit rating		29					29
Credit Exposure Under Off System Sales		1					1
Delmarva Power and Light Company [Member]
Derivative [Line Items]
Income taxes		19		9			18		34
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							98.00%
Expected Generation Hedged In Year Two							85.00%
Expected generation hedged in year three							54.00%
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							88.00%
Expected generation hedged in year three							57.00%
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		3					3
Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative, Notional Amount											$ 100
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		672					672
Designated as Hedging Instrument [Member] | Commonwealth Edison Co [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	[2]	(244)					(244)			(247)
Mark-to-market derivative liabilities (noncurrent liabilities)		(225)					(225)			224
Derivative Liability, Current		(19)					(19)			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		85					85
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		744					744			1,506
Mark-to-market derivative liabilities (noncurrent liabilities)		412					412			366
Derivative Liability, Current		213					213			197
Derivative [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	[3]	988					988			1,753
Mark-to-market derivative liabilities (noncurrent liabilities)	[3]	187					187			142
Derivative Liability, Current	[3]	194					194			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							39			$ 25
Cash Flow Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		90					90
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							176
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
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		496					496
ExGen Texas Power [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities (noncurrent liabilities)		15					15
Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Income taxes	[5]	0					0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes	[5]	0					0
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]			(1)			2		(13)
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				$ (1)	[5]		2	[5]	3
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)		$ (10)
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		24					24
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility		45					45
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		22					22
Potomac Electric Power Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		47					47
Delmarva Power and Light Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		12					12
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		$ 10					$ 10

[1] For the nine months ended September 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.