Derivative Financial Instruments - Narrative (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2016 USD ($) GWh		Dec. 31, 2015 USD ($) GWh		Dec. 31, 2014 USD ($) GWh	Mar. 31, 2016 USD ($)
Derivative [Line Items]
Proprietary trading activities volume | GWh			6,179		7,310		10,571
Derivative, notional amount			$ 2,918,000		$ 1,774,000
Pre-tax net income impact associated with a hypothetical 10% increase in interest rates - exclusive upper bound			7,000
Ineffective portion recognized in income			14,000		17,000
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	$ 3,000
Derivative, Gain (Loss) on Derivative, Net	3,000
Mark-to-market derivative liabilities			392,000		374,000
Mark-to-market derivative liabilities			282,000		205,000
Derivative, collateral, right to reclaim cash			29,000		52,000
Cash collateral held			(9,000)
Letters of credit held			16,000
Interest Rate Fair Value Hedge Asset at Fair Value			16,000
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional amount of preissuance interest rate cash flow hedge derivatives			659,000
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, notional amount	100,000		800,000					$ 600,000
Derivative Asset			28,000		54,000
Mark-to-market derivative liabilities			4,000		8,000
Mark-to-market derivative liabilities			8,000		8,000
Interest Rate Swap [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative, notional amount	90,000							100,000
Interest Rate Swap [Member] | PHI Merger [Member]
Derivative [Line Items]
Derivative, notional amount		$ 2,400,000
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset			16,000
Mark-to-market derivative liabilities			0
Mark-to-market derivative liabilities			0
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Derivative, notional amount			800,000		800,000
Derivative Asset			16,000		25,000
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | ExGen Texas Power [Member]
Derivative [Line Items]
Derivative, notional amount			495,000
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | ExGen Texas Power [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities			9,000
Derivative [Member]
Derivative [Line Items]
Derivative Asset			1,381,000		2,069,000
Mark-to-market derivative liabilities			388,000		366,000
Mark-to-market derivative liabilities			274,000		197,000
Designated as Hedging Instrument [Member] | PHI Merger [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net		$ (64,000)
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Net receivable from electric utility			26,000
Credit exposure under off system sales			8,000
Incremental collateral for loss of investment grade credit rating			62,000
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities			153,000		150,000
Mark-to-market derivative liabilities			263,000		182,000
Derivative, collateral, right to reclaim cash			8,000		3,000
Letters of credit posted			284,000		497,000
Cash collateral held			(24,000)		(21,000)
Letters of credit held			28,000		78,000
Cash collateral posted			347,000		1,267,000
Incremental collateral for loss of investment grade credit rating			1,900,000		2,000,000
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member] | Other Solar Projects [Member]
Derivative [Line Items]
Notional amount of interest rate swaps acquired from merger								24,000
Exelon Generation Co L L C [Member] | Total Cash Flow Hedges [Member]
Derivative [Line Items]
Cash flow hedge activity impact on pre-tax net income based on reclassification adjustment from accumulated other comprehensive income					2,000		$ 195,000
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Asset			12,000		29,000
Mark-to-market derivative liabilities			4,000		8,000
Mark-to-market derivative liabilities			8,000		8,000
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Other Solar Projects [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Notional amount of interest rate swaps acquired from merger								$ 25,000
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset			0		0
Mark-to-market derivative liabilities			3,000		8,000
Mark-to-market derivative liabilities			7,000		8,000
Exelon Generation Co L L C [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, notional amount			164,000
Exelon Generation Co L L C [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities			1,000
Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, notional amount			85,000
Exelon Generation Co L L C [Member] | Derivative [Member]
Derivative [Line Items]
Derivative Asset			1,381,000	[1]	2,069,000	[2]
Mark-to-market derivative liabilities			149,000	[1]	142,000	[2]
Mark-to-market derivative liabilities			$ 255,000	[1]	174,000	[2]
Commonwealth Edison Co [Member]
Derivative [Line Items]
Term of contract			20 years
Mark-to-market derivative liabilities			$ (239,000)		224,000
Mark-to-market derivative liabilities			19,000		23,000
Net receivable from electric utility			14,000
Credit exposure under off system sales			1,000
Cash collateral held			(3,000)
Letters of credit held			19,000
Incremental collateral for loss of investment grade credit rating			19,000
PECO Energy Co [Member]
Derivative [Line Items]
Net receivable from electric utility			33,000
Incremental collateral for loss of investment grade credit rating			31,000
Pepco Holdings LLC [Member] | Predecessor [Member]
Derivative [Line Items]
Derivative Asset					18,000
Mark-to-market derivative liabilities					0
Mark-to-market derivative liabilities					0
Pepco Holdings LLC [Member] | Derivative [Member] | Successor [Member]
Derivative [Line Items]
Derivative Asset			0
Mark-to-market derivative liabilities			0
Mark-to-market derivative liabilities			0
Potomac Electric Power Company [Member]
Derivative [Line Items]
Net receivable from electric utility			44,000
Delmarva Power and Light Company [Member]
Derivative [Line Items]
Net receivable from electric utility			16,000
Incremental collateral for loss of investment grade credit rating			10,000
Delmarva Power and Light Company [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Brokered Natural Gas Margin Revenue			2,750
Delmarva Power and Light Company [Member] | Derivative [Member]
Derivative [Line Items]
Derivative Asset			0		0	[2]
Mark-to-market derivative liabilities			0		0	[2]
Mark-to-market derivative liabilities			0		$ 0	[2]
Atlantic City Electric Company [Member]
Derivative [Line Items]
Net receivable from electric utility			$ 9,000
Minimum [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months			91.00%
Expected generation hedged in year two			56.00%
Expected generation hedged in year three			28.00%
Minimum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged			10.00%
Maximum [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months			94.00%
Expected generation hedged in year two			59.00%
Expected generation hedged in year three			31.00%
Maximum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged			20.00%
Senior Notes [Member]
Derivative [Line Items]
Debt Instrument, Face Amount	$ 4,200,000
Senior Notes [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Debt Instrument, Face Amount			$ 750,000

[1] 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.

[2] 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.