Derivative Financial Instruments - Narrative (Details) $ in Thousands		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2017 USD ($) GWh	Jun. 30, 2016 USD ($) GWh	Jun. 30, 2017 USD ($) GWh	Jun. 30, 2016 USD ($) GWh	Dec. 31, 2016 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)
Derivative [Line Items]
Income taxes		$ (72,000)	$ 102,000	$ 143,000	$ 285,000
Derivative, Notional Amount			100,000		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				3,000
Ineffective portion recognized in income		3,000	4,000	7,000	6,000
Mark-to-market derivative liabilities (noncurrent liabilities)		417,000		417,000		$ 392,000
Cash collateral posted		19,000		19,000
Letters of credit posted		10,000		10,000
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes		(158,000)	$ (31,000)	(31,000)	$ 120,000
Mark-to-market derivative liabilities (noncurrent liabilities)		180,000		180,000		153,000
Cash collateral received not offset against net derivative positions		(2,000)		(2,000)		(8,000)
Cash collateral posted		517,000		517,000		347,000
Letters of credit held		21,000		21,000		28,000
Letters of credit posted		278,000		278,000		284,000
Cash collateral held		34,000		34,000		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		$ (3,000)		$ (3,000)
Derivative, Nonmonetary Notional Amount, Energy Measure | GWh		2,312	1,289	4,162	2,509
Commonwealth Edison Company [Member]
Derivative [Line Items]
Cash collateral held		$ 13,000		$ 13,000
Commonwealth Edison Co [Member]
Derivative [Line Items]
Income taxes		104,000	$ 91,000	197,000	$ 168,000
Mark-to-market derivative liabilities (noncurrent liabilities)		237,000		237,000		239,000
Cash collateral held		19,000		19,000
Incremental collateral for loss of investment grade credit rating		12,000		12,000
Credit Exposure Under Off System Sales		1,000		1,000
PECO Energy Co [Member]
Derivative [Line Items]
Income taxes		20,000	23,000	$ 55,000	67,000
Estimated percentage of natural gas purchases hedged				20.00%
Incremental collateral for loss of investment grade credit rating		21,000		$ 21,000
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Income taxes		31,000	6,000	111,000	73,000
Incremental collateral for loss of investment grade credit rating		36,000		36,000
Credit Exposure Under Off System Sales		1,000		1,000
Delmarva Power and Light Company [Member]
Derivative [Line Items]
Income taxes		12,000	$ 8,000	24,000	(1,000)
Incremental collateral for loss of investment grade credit rating		10,000		$ 10,000
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				71.00%
Expected generation hedged in year three				39.00%
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				74.00%
Expected generation hedged in year three				42.00%
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
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		492,000		492,000
Foreign Exchange Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Notional Amount		103,000		103,000
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		628,000		628,000		719,000
Mark-to-market derivative liabilities (noncurrent liabilities)		416,000		416,000		388,000
Derivative [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	[1]	884,000		884,000		977,000
Mark-to-market derivative liabilities (noncurrent liabilities)	[1]	179,000		179,000		149,000
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)	[2]	0		0		0
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net		8,000		8,000		16,000
Mark-to-market derivative liabilities (noncurrent liabilities)		1,000		1,000		4,000
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net		(3,000)		(3,000)		0
Mark-to-market derivative liabilities (noncurrent liabilities)		1,000		1,000		4,000
Fair Value Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		800,000		800,000		800,000
Increase (Decrease) in Fair Value of Interest Rate Fair Value Hedging Instruments				11,000		$ 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		492,000		492,000
ExGen Texas Power [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities (noncurrent liabilities)		8,000		8,000
ExGen Renewables [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount							$ 164,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Income taxes	[3]			(3,000)	(2,000)
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		0
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
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]			3,000	2,000
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes	[3]			3,000	$ 2,000
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		23,000		23,000
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility		27,000		27,000
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		21,000		21,000
Potomac Electric Power Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		41,000		41,000
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		$ 6,000		$ 6,000

[1] Current and noncurrent assets are shown net of collateral of $149 million and $74 million, respectively, and current and noncurrent liabilities are shown net of collateral of $155 million and $107 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $485 million at June 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.