Derivative Financial Instruments - Narrative (Details) MWh in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) MWh		Dec. 31, 2014 USD ($) MWh		Dec. 31, 2013 USD ($) MWh	Jun. 30, 2015 USD ($)
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	30.00%
Derivative, notional amount	$ 1,774		$ 1,491
Pre-tax net income impact associated with a hypothetical 10% increase in interest rates - exclusive upper bound	6
Ineffective portion recognized in income	17		18
Notional amount of interest rate swaps acquired from merger	2,400
Mark-to-market derivative liabilities	374		403
Mark-to-market derivative liabilities	205		234
Derivative, collateral, right to reclaim cash	52		43
Cash collateral held	13
Letters of credit held	69
Net Asset Liability Position After Contractual Right Of Offset	38
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional amount of preissuance interest rate cash flow hedge derivatives	738
Reclassification out of Accumulated Other Comprehensive Income [Member] | Energy Related Hedges [Member] | Operating Revenue One [Member]
Derivative [Line Items]
Cash flow hedge activity impact on pre-tax net income based on reclassification adjustment from accumulated other comprehensive income	2		195		$ 464
Designated as Hedging Instrument [Member] | PHI Merger [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	64
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Derivative, notional amount	800		1,450
Derivative Asset	25		29
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | ExGen Texas Power [Member]
Derivative [Line Items]
Derivative, notional amount	500
Interest Rate Swap [Member] | Derivative [Member]
Derivative [Line Items]
Derivative, notional amount	800
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	12
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	26
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Notional amount of preissuance interest rate cash flow hedge derivatives			400
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Net receivable from electric utility	31
Credit exposure under off system sales	4
Incremental collateral for loss of investment grade credit rating	$ 35
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net			$ 4
Proprietary trading activities volume | MWh	10,571		8,762		12,958
Hypothetical increase in interest rates associated with variable-rate debt	50.00%
Mark-to-market derivative liabilities	$ 150		$ 105
Mark-to-market derivative liabilities	182		214
Derivative, collateral, right to reclaim cash	3		8
Letters of credit posted	497		672
Cash collateral held	21		77
Letters of credit held	78		24
Cash collateral posted			1,497
Incremental collateral for loss of investment grade credit rating	2,000		2,400
Net Asset Liability Position After Contractual Right Of Offset	13
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset	7,096		6,813
Mark-to-market derivative liabilities	1,673		1,540
Mark-to-market derivative liabilities	4,907		4,947
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member] | Other Solar Projects [Member]
Derivative [Line Items]
Derivative, notional amount	24
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		195		$ 683
Exelon Generation Co L L C [Member] | Derivative [Member]
Derivative [Line Items]
Derivative, collateral, right to reclaim cash	1,267
Exelon Generation Co L L C [Member] | Derivative [Member] | Other Solar Projects [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities	2
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities	2
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Derivative, notional amount			550
Derivative Asset			7
Exelon Generation Co L L C [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Derivative, notional amount	189
Notional amount of interest rate swaps acquired from merger	25
Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, notional amount	$ 30
Commonwealth Edison Co [Member]
Derivative [Line Items]
Term of contract	20 years
Mark-to-market derivative liabilities	$ 224		187
Mark-to-market derivative liabilities	23		20
Net receivable from electric utility	15
Cash collateral held	19
Commonwealth Edison Co [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Asset	0	[1]	0
Mark-to-market derivative liabilities	224	[1]	187	[2]
Mark-to-market derivative liabilities	23	[1]	$ 20	[2]
PECO Energy Co [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities	12
Net receivable from electric utility	36
Incremental collateral for loss of investment grade credit rating	$ 25
Minimum [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months	90.00%
Expected generation hedged in year two	60.00%
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	93.00%
Expected generation hedged in year two	63.00%
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	$ 3,300					$ 4,200
Senior Notes [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Debt Instrument, Face Amount	$ 750

[1] Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers.

[2] Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers.