Derivative Financial Instruments - Narrative (Details) $ in Millions		3 Months Ended		6 Months Ended	12 Months Ended
		Mar. 31, 2016 USD ($) GWh	Mar. 31, 2015 USD ($) GWh	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($)
Derivative [Line Items]
Income taxes		$ 184	$ 363
Hypothetical Increase In Interest Rates		0.50%
Derivative, Notional Amount		$ 600
Derivative Asset, Noncurrent		841				$ 758
Hypothetical increase in interest rates associated with variable-rate debt		1
Ineffective portion recognized in income	[1]	2
Mark-to-market derivative liabilities (noncurrent liabilities)		408				374
Derivative Liability, Current		203				205
Cash collateral posted		8
Letters of credit posted		87
Interest Rate Fair Value Hedge Asset at Fair Value		40
Debt Instrument, Face Amount			750
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount of Pre-issuance Interest Rate Cash Flow Hedge Derivatives		1,287
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes		$ 151	$ 226
Proprietary trading activities volume | GWh		1,220	1,808
Derivative Asset, Noncurrent		$ 799				733
Mark-to-market derivative liabilities (noncurrent liabilities)		166				150
Derivative Liability, Current		177				182
Cash collateral received not offset against net derivative positions		1				3
Cash collateral posted		1,063				1,267
Letters of credit held		96				78
Letters of credit posted		519				497
Cash collateral held		16				21
Incremental collateral for loss of investment grade credit rating		1,900				2,000
Interest Rate Fair Value Hedge Asset at Fair Value		1
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount of Pre-issuance Interest Rate Cash Flow Hedge Derivatives		687
Commonwealth Edison Co [Member]
Derivative [Line Items]
Income taxes		77	$ 59
Mark-to-market derivative liabilities (noncurrent liabilities)		239				224
Derivative Liability, Current		26				23
Cash collateral held		19
Incremental collateral for loss of investment grade credit rating		17
PECO Energy Co [Member]
Derivative [Line Items]
Income taxes		$ 43	58
Estimated percentage of natural gas purchases hedged		30.00%
Incremental collateral for loss of investment grade credit rating		$ 22
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Income taxes		66	74
Incremental collateral for loss of investment grade credit rating		28
Credit Exposure Under Off System Sales		2
Delmarva Power and Light Company [Member]
Derivative [Line Items]
Income taxes		$ (9)	21
Minimum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months		96.00%
Expected Generation Hedged In Year Two		69.00%
Expected generation hedged in year three		37.00%
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		99.00%
Expected Generation Hedged In Year Two		72.00%
Expected generation hedged in year three		40.00%
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
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Liability, Current		3
Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative, Notional Amount		100
Derivative Asset, Noncurrent		3
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Total mark-to-market derivative net assets (liabilities)		602				516
Designated as Hedging Instrument [Member] | Commonwealth Edison Co [Member]
Derivative [Line Items]
Total mark-to-market derivative net assets (liabilities)	[2]	(265)				(247)
Designated as Hedging Instrument [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Total mark-to-market derivative net assets (liabilities)		(1)				(2)
Foreign Exchange Contract [Member] | Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		137
Energy Related Derivative [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Brokered Natural Gas Margin Revenue		3
Fair Value Hedging [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		800				$ 800
Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments		42			$ 25
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Increase In Notional Amount Of Derivative Instruments		189
Other Solar Projects [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Notional amounts on forward starting interest rate swaps		25
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		24
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
ExGen Texas Power [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		499
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)		17
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	[3]	(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	[3]	(2)
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	[3]	(2)
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		19
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility		37
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		35
Delmarva Power and Light Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		11
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		$ 8

[1] For the three months ended March 31, 2015, the loss on Generation swaps included $1 million realized in earnings with an immaterial amount excluded from hedge effectiveness testing.

[2] .

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