Derivative Financial Instruments - Narrative (Details) $ in Thousands		3 Months Ended			6 Months Ended	9 Months Ended
		Sep. 30, 2017 USD ($) GWh		Sep. 30, 2016 USD ($) GWh	Jun. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) GWh		Sep. 30, 2016 USD ($) GWh	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)		Mar. 31, 2016 USD ($)
Derivative [Line Items]
Income taxes		$ 452,000		$ 340,000		$ 595,000		$ 625,000
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
Ineffective portion recognized in income		4,000		6,000		11,000		12,000
Mark-to-market derivative liabilities (noncurrent liabilities)		410,000				410,000				$ 392,000
Cash collateral posted		19,000				19,000
Letters of credit posted		12,000				12,000
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes		240,000		$ 173,000		209,000		$ 293,000
Mark-to-market derivative liabilities (noncurrent liabilities)		153,000				153,000				153,000
Cash collateral received not offset against net derivative positions		(3,000)				(3,000)				(8,000)
Cash collateral posted		460,000				460,000				347,000
Letters of credit held		29,000				29,000				28,000
Letters of credit posted		255,000				255,000				284,000
Cash collateral held		49,000				49,000				24,000
Incremental collateral for loss of investment grade credit rating		1,800,000				1,800,000				1,900,000
Interest Rate Fair Value Hedge Asset at Fair Value		$ (4,000)				$ (4,000)
Derivative, Nonmonetary Notional Amount, Energy Measure | GWh		2,601		1,506		6,763		4,015
Commonwealth Edison Company [Member]
Derivative [Line Items]
Cash collateral held		$ 10,000				$ 10,000
Commonwealth Edison Co [Member]
Derivative [Line Items]
Income taxes		131,000		$ 75,000		328,000		$ 244,000
Mark-to-market derivative liabilities (noncurrent liabilities)		257,000				257,000				239,000
Cash collateral held		21,000				21,000
Incremental collateral for loss of investment grade credit rating		3,000				3,000
Credit Exposure Under Off System Sales		1,000				1,000
PECO Energy Co [Member]
Derivative [Line Items]
Income taxes		28,000		54,000		$ 84,000		121,000
Estimated percentage of natural gas purchases hedged						20.00%
Incremental collateral for loss of investment grade credit rating		20,000				$ 20,000
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Income taxes		40,000		36,000		151,000		109,000
Incremental collateral for loss of investment grade credit rating		28,000				28,000
Credit Exposure Under Off System Sales		1,000				1,000
Delmarva Power and Light Company [Member]
Derivative [Line Items]
Income taxes		19,000		19,000		43,000		18,000
Incremental collateral for loss of investment grade credit rating		9,000				$ 9,000
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						79.00%
Expected generation hedged in year three						45.00%
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						82.00%
Expected generation hedged in year three						48.00%
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				$ 800,000			$ 164,000
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]
Derivative, Notional Amount		491,000				491,000
Foreign Exchange Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Notional Amount		111,000				111,000
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		531,000				531,000				719,000
Mark-to-market derivative liabilities (noncurrent liabilities)		409,000				409,000				388,000
Derivative Asset		1,110,000				1,110,000				1,381,000
Derivative [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net		808,000	[1]			808,000	[1]			977,000	[2]
Mark-to-market derivative liabilities (noncurrent liabilities)		152,000	[1]			152,000	[1]			149,000	[2]
Derivative Asset		1,110,000	[1]			1,110,000	[1]			1,381,000	[2]
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)		0				0				0
Derivative Asset		0				0				0
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net		6,000				6,000				16,000
Mark-to-market derivative liabilities (noncurrent liabilities)		1,000				1,000				4,000
Derivative Asset		15,000				15,000				28,000
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net		(4,000)				(4,000)				0
Mark-to-market derivative liabilities (noncurrent liabilities)		1,000				1,000				4,000
Derivative Asset		5,000				5,000				12,000
Fair Value Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		800,000				800,000				800,000
Derivative Asset		10,000				10,000				$ 16,000
ExGen Texas Power [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		491,000				491,000
ExGen Texas Power [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities (noncurrent liabilities)		6,000				6,000
Derivative, Gain (Loss) on Derivative, Net		(2,000)				2,000
Sacramento PV Energy [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount												25,000
Constellation Solar Horizons Financing [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount												$ 24,000
Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Income taxes	[3]			0				0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes	[3]			0				0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Income taxes		1,000				(2,000)		(2,000)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Income taxes	[3]	(1,000)		1,000		2,000		3,000
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes	[3]	(1,000)		$ 1,000		2,000		$ 3,000
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		18,000				18,000
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility		22,000				22,000
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		22,000				22,000
Potomac Electric Power Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		34,000				34,000
Delmarva Power and Light Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		12,000				12,000
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		$ 7,000				$ 7,000

[1] Current and noncurrent assets are shown net of collateral of $123 million and $61 million, respectively, and current and noncurrent liabilities are shown net of collateral of $138 million and $93 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $415 million at September 30, 2017.

[2] 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.

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