Derivative Financial Instruments - Narrative (Details) $ in Thousands		3 Months Ended			12 Months Ended
		Mar. 31, 2017 USD ($) GWh	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($) GWh	Dec. 31, 2016 USD ($)
Derivative [Line Items]
Income taxes		$ 215,000		$ 184,000
Derivative, Notional Amount			$ 100,000	600,000
Derivative, Loss on Derivative			3,000
Derivative Instruments, Loss Recognized in Other Comprehensive Income (Loss), Effective Portion			$ 3,000
Hypothetical increase in interest rates associated with variable-rate debt		2,000
Ineffective portion recognized in income	[1]	4,000		2,000
Mark-to-market derivative liabilities (noncurrent liabilities)		420,000			$ 392,000
Cash collateral posted		23,000
Letters of credit posted		10,000
Interest Rate Fair Value Hedge Asset at Fair Value		(9,000)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes		127,000		$ 151,000
Mark-to-market derivative liabilities (noncurrent liabilities)		157,000			153,000
Cash collateral received not offset against net derivative positions		(8,000)
Cash collateral posted		471,000			347,000
Letters of credit held		32,000			28,000
Letters of credit posted		273,000			284,000
Cash collateral held		35,000			24,000
Incremental collateral for loss of investment grade credit rating		1,800,000			1,900,000
Interest Rate Fair Value Hedge Asset at Fair Value		$ (3,000)
Derivative, Nonmonetary Notional Amount, Energy Measure | GWh		1,850		1,220
Commonwealth Edison Company [Member]
Derivative [Line Items]
Cash collateral held		$ 1,000
Commonwealth Edison Co [Member]
Derivative [Line Items]
Income taxes		92,000		$ 77,000
Mark-to-market derivative liabilities (noncurrent liabilities)		263,000			239,000
Cash collateral held		19,000
Incremental collateral for loss of investment grade credit rating		10,000
Credit Exposure Under Off System Sales		1,000
PECO Energy Co [Member]
Derivative [Line Items]
Income taxes		$ 36,000		43,000
Estimated percentage of natural gas purchases hedged		25.00%
Incremental collateral for loss of investment grade credit rating		$ 27,000
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Income taxes		80,000		66,000
Incremental collateral for loss of investment grade credit rating		47,000
Credit Exposure Under Off System Sales		3,000
Delmarva Power and Light Company [Member]
Derivative [Line Items]
Income taxes		11,000		(9,000)
Incremental collateral for loss of investment grade credit rating		$ 11,000
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		60.00%
Expected generation hedged in year three		30.00%
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		63.00%
Expected generation hedged in year three		33.00%
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		$ 800,000
Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative, Notional Amount				100,000
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		657,000
Designated as Hedging Instrument [Member] | Commonwealth Edison Co [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	[2]	(282,000)			(258,000)
Mark-to-market derivative liabilities (noncurrent liabilities)		263,000			239,000
Designated as Hedging Instrument [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Derivative, Fair Value, Net		0			2,000
Mark-to-market derivative liabilities (noncurrent liabilities)		0			0
Foreign Exchange Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Notional Amount		73,000
Energy Related Derivative [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Brokered Natural Gas Margin Revenue		2,750
Derivative [Member]
Derivative [Line Items]
Derivative, Fair Value, Net		729,000			719,000
Mark-to-market derivative liabilities (noncurrent liabilities)		416,000			388,000
Derivative [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	[3]	1,011,000			977,000
Mark-to-market derivative liabilities (noncurrent liabilities)	[3]	153,000			149,000
Derivative [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Derivative, Fair Value, Net		0			0
Mark-to-market derivative liabilities (noncurrent liabilities)	[4]	0			0
Fair Value Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		800,000			800,000
Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments		12,000			$ 16,000
Other Solar Projects [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Notional amounts on forward starting interest rate swaps				25,000
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				24,000
ExGen Texas Power [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		494,000
ExGen Texas Power [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities (noncurrent liabilities)		7,000
ExGen Renewables [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		164,000
ExGen Renewables [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities (noncurrent liabilities)		1,000
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]	(3,000)		$ (2,000)
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		13,000
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility		31,000
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		24,000
Potomac Electric Power Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		40,000
Delmarva Power and Light Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		13,000
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		$ 7,000

[1] Three Months Ended March 31, Income StatementLocation 2017 2016 2017 2016 Gain (loss) on Swaps Gain (loss) on BorrowingsExelonInterest expense $(4) $17 $8 $(15)

[2] .

[3] .

[4] Current and noncurrent assets are shown net of collateral of $100 million and $72 million, respectively, and current and noncurrent liabilities are shown net of collateral of $95 million and $62 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $329 million at December 31, 2016.

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