Regulatory Matters - Narrative (Details) (USD $)	1 Months Ended		12 Months Ended		0 Months Ended							1 Months Ended		3 Months Ended	9 Months Ended	12 Months Ended		0 Months Ended					1 Months Ended	0 Months Ended						1 Months Ended	12 Months Ended	60 Months Ended	65 Months Ended	0 Months Ended	1 Months Ended	3 Months Ended	0 Months Ended
	Jan. 31, 2014	Sep. 30, 2008	Dec. 31, 2014 V	Dec. 31, 2013 MW	Dec. 11, 2014	Apr. 16, 2014	Dec. 19, 2013	Jun. 30, 2013	Apr. 29, 2013	Dec. 19, 2012	Jul. 31, 2012	Apr. 30, 2014	Apr. 30, 2013	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2012	Dec. 31, 2011	Dec. 02, 2013 V mi	Mar. 29, 2013	Mar. 15, 2013	Dec. 05, 2012 MWh	Aug. 09, 2011	Sep. 30, 2012	Dec. 08, 2014	Oct. 17, 2014	Aug. 23, 2014	Dec. 13, 2013	Feb. 27, 2013	Feb. 22, 2013	Aug. 31, 2010 smart_meter	Dec. 31, 2007	Nov. 30, 2010	Nov. 30, 2005	Apr. 12, 2012	Mar. 31, 2011	Dec. 31, 2014	Jan. 13, 2015	Mar. 31, 2013	Sep. 18, 2014	Apr. 01, 2014	Mar. 31, 2014	Oct. 31, 2013	Apr. 01, 2013	Dec. 20, 2012	Jun. 02, 2011	Aug. 15, 2013	Jun. 19, 2013 smart_meter	Dec. 16, 2010	Jun. 01, 2009	Sep. 15, 2014	Aug. 21, 2014	Jul. 02, 2014	Apr. 28, 2014	Apr. 27, 2014	Feb. 26, 2014	Aug. 23, 2013	Feb. 28, 2010	Jun. 03, 2014
Regulatory Matters Additional Narrative Information [Line Items]
Revenue reduction	$ 8,000,000
Electric revenues increase order		274,000,000
Substation kilovolt			500,000
Near zero emissions coal fueled generation plant				166
Parent company pension OPEB regulatory assets noncurrent			3,256,000,000																																	3,256,000,000
Noncurrent regulatory assets			6,076,000,000	5,910,000,000																																6,076,000,000
Regulatory liabilities			310,000,000	327,000,000																																310,000,000
Business Combination, Integration Related Costs			19,000,000	28,000,000
Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities			25,000,000	53,000,000																																25,000,000
Under Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			11,000,000	9,000,000																																11,000,000
Energy Efficiency And Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			159,000,000	148,000,000																																159,000,000
Non-severance Merger Integration Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory assets				4,000,000
Amortization period			P5Y
Merger Integration Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amortization period			5
Noncurrent regulatory assets			6,000,000	9,000,000																																6,000,000
Regulatory asset recovery, period one																																						4,000,000
Regulatory asset recovery, period two																																						4,000,000
Electric Generation Related Regulatory Asset [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			20,000,000	30,000,000																																20,000,000
Deferred Storm Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			2,000,000	3,000,000																																2,000,000
Severance Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amortization period			P5Y
Net regulatory assets																35,000,000
Under Recovered Distribution Service Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			120,000,000	285,000,000																																120,000,000
AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amortization period			ten
Noncurrent regulatory assets			271,000,000	159,000,000																																271,000,000
Asset Retirement Obligations [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			115,000,000	102,000,000																																115,000,000
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Additional revenue requirement allowed by updated government order			88,000,000	35,000,000	232,000,000	269,000,000	341,000,000		353,000,000	73,000,000		22,000,000	68,000,000
Current year revenue adjustment			160,000,000	160,000,000								36,000,000	38,000,000			80,000,000
Prior year revenue adjustment			72,000,000									14,000,000	30,000,000			(181,000,000)	(7,000,000)
Weighted average debt and equity return					7.06%		6.94%																															8.91%		8.62%	8.70%		8.70%	7.54%
Rate of return on common equity			9.25%				8.72%			9.81%				11.50%
Annual revenue requirement reduction								14,000,000
Contribution to technology innovation trust											15,000,000
Subsequent contribution to technology innovation trust											4,000,000
Utility annual customer assistance											10,000,000
Smart meters installed			550,000
Rate of return on common equity electric distribution		10.30%
Estimated refund obligation to customers																																													37,000,000
Collections under rider AMP			24,000,000																																	24,000,000			9,500,000			14,600,000
Purchased accounts receivables for PORCB			139,000,000																																	139,000,000
Term of contract			20 years
Annual energy savings requirement			0.20%																																	0.20%
Demand response peak demand reduction			2.00%																																	2.00%
Low income sector consumption reduction targets Act 129 Phase II			0.10%
Renewable energy procurement			2.00%																																	2.00%
Noncurrent regulatory assets			852,000,000	933,000,000																																852,000,000
Common equity component cap															55.00%
Regulatory liabilities			125,000,000	170,000,000																																125,000,000
Under over recovered distribution service costs				377,000,000
Customer refundable fees			3,000,000	37,000,000																																3,000,000
Customer refundable fees, interest			1,000,000	1,000,000																																1,000,000
Commonwealth Edison Co [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Under over recovered distribution service costs			286,000,000
Cost recovery for significant one-time events			85,000,000	86,000,000
Commonwealth Edison Co [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Renewable energy resources cumulatively increase			10.00%
Commonwealth Edison Co [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Renewable energy resources cumulatively increase			25.00%
Commonwealth Edison Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities			25,000,000	45,000,000																																25,000,000
Commonwealth Edison Co [Member] | Energy Related Derivative [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Term of contract			20 years
Commonwealth Edison Co [Member] | FutureGen Industry Alliance [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Term of contract				20 years
Commonwealth Edison Co [Member] | Northern Illinois Project [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Length of transmission line																		60
Substation kilovolt																		345,000
Commonwealth Edison Co [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			7,000,000	6,000,000																																7,000,000
Commonwealth Edison Co [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			0	0																																0
Commonwealth Edison Co [Member] | Merger Integration Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory assets			7,000,000	6,000,000																																7,000,000
Noncurrent regulatory assets			0	0																																0
Commonwealth Edison Co [Member] | Electric Generation Related Regulatory Asset [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			0	0																																0
Commonwealth Edison Co [Member] | Deferred Storm Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			0	0																																0
Commonwealth Edison Co [Member] | Transmission Rate Formula [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Net regulatory assets			21,000,000	17,000,000																																21,000,000
Commonwealth Edison Co [Member] | Severance Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Net regulatory assets																16,000,000
Commonwealth Edison Co [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			120,000,000	285,000,000																																120,000,000
Regulatory assets due to deferred storm costs			66,000,000	58,000,000																																66,000,000
Commonwealth Edison Co [Member] | AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			81,000,000	35,000,000																																81,000,000
Commonwealth Edison Co [Member] | Asset Retirement Obligations [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Net regulatory asset			371,000,000	463,000,000																																371,000,000
Noncurrent regulatory assets			73,000,000	67,000,000																																73,000,000
Commonwealth Edison Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Electric Transmission Costs Under-Recovery			3,000,000																																	3,000,000
Commonwealth Edison Company [Member] | Renewable Energy Program [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities			16,000,000	9,000,000																																16,000,000
Commonwealth Edison Company [Member] | Under-Recovered Electric Supply Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Electric Transmission Costs Under-Recovery			4,000,000	35,000,000																																4,000,000
Commonwealth Edison Company [Member] | Over Recovered Electric Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities			19,000,000																																	19,000,000
Commonwealth Edison Company [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory assets			33,000,000	58,000,000																																33,000,000
Electric Transmission Costs Under-Recovery			22,000,000	17,000,000																																22,000,000
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Low income sector consumption reduction targets Act 129 Phase II																					4.50%
Increase in electric delivery service revenue resulting from rate case settlement or order.																																																225,000,000
Increase in gas delivery service revenue resulting from rate case settlement or order.																																																20,000,000
Electric distribution tax repairs																						171,000,000
Gas distribution tax repairs refund																							54,000,000
Smart meters initial phase deployment			1,600,000.0																																	1,600,000.0
Estimated number of smart meters to be installed			1,700,000																																	1,700,000											600,000
Projected investment in smart meters			583,000,000																																	583,000,000
Projected investment in smart grid infrastructure			155,000,000																																	155,000,000
Total smart grid smart meter investment grant awarded			200,000,000																																	200,000,000
Total smart meter spend on investment			540,000,000																																	540,000,000
Total smart grid spend on investment			119,000,000																																	119,000,000
Smart grid investment grant awarded			60,000,000																																	60,000,000
Smart grid sub recipient investment			4,000,000																																	4,000,000
Smart meter investment grant awarded			140,000,000																																	140,000,000
Carrying value of smart meters excluding DOE reimbursements			17,000,000																																	17,000,000
DOE reimbursements use for original meter installment			16,000,000																																	16,000,000
Depreciation related to original meters			2,000,000
Vendor refund																																														12,000,000
Cost recoveries sought under direct load control program																			12,000,000
Cumulative consumption reduction targets																					1,125,852
Public sector maximum consumption reduction targets Act 129 Phase II																					10.00%
Proposed funding Of direct load control program costs																				10,000,000
Total alternative energy credits purchased annually			452,000
Solar tier 1 alternative energy credits purchased annually			8,000
Noncurrent regulatory assets			1,529,000,000	1,448,000,000																																1,529,000,000
Regulatory liabilities			90,000,000	106,000,000																																90,000,000
PECO Energy Co [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Annual energy savings requirement																																																	3.00%
Demand response peak demand reduction																																																	4.50%
PECO Energy Co [Member] | OverRecoveredNaturalGasSupply [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities			16,000,000	16,000,000																																16,000,000
PECO Energy Co [Member] | DSP Program costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities			39,000,000	34,000,000																																39,000,000
PECO Energy Co [Member] | Over-Recovered Electric Transmission Cost [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities			3,000,000	8,000,000																																3,000,000
PECO Energy Co [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Percentage Tier I alternative energy resources																	3.50%
Percentage Tier II alternative energy resources																	6.20%
PECO Energy Co [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Low income sector consumption reduction targets Act 129 Phase II																					2.00%
Percentage Tier I alternative energy resources																	8.00%
Percentage Tier II alternative energy resources																	10.00%
PECO Energy Co [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Maximum civil penalty under Act 129																					20,000,000
PECO Energy Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities			0	8,000,000																																0
PECO Energy Co [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			0	0																																0
PECO Energy Co [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			0	0																																0
PECO Energy Co [Member] | Merger Integration Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			0	0																																0
PECO Energy Co [Member] | Electric Generation Related Regulatory Asset [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			0	0																																0
PECO Energy Co [Member] | Deferred Storm Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			0	0																																0
PECO Energy Co [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			0	0																																0
PECO Energy Co [Member] | AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amortization period			P10Y
Noncurrent regulatory assets			62,000,000	58,000,000																																62,000,000
PECO Energy Co [Member] | Asset Retirement Obligations [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			26,000,000	25,000,000																																26,000,000
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Weighted average debt and equity return																																																					8.53%	8.35%
Rate of return on common equity															11.30%
Increase in electric delivery service revenue resulting from rate case settlement or order.				34,000,000
Increase in gas delivery service revenue resulting from rate case settlement or order.				12,000,000
Estimated number of smart meters to be installed																														2,000,000
Requested increase in electric revenues																									22,000,000				81,000,000																					99,000,000
Requested increase in gas revenues																									38,000,000				32,000,000																							68,000,000
Annual depreciation expense decrease regulated property																									20,000,000
Adjustment to electric revenues increase requested																																																								83,000,000
Public utilities, requested rate increase (decrease), amount																										24,000,000
Requested rate of return on common equity																											9.75%		9.75%
Rate of return common equity gas distribution																											9.60%		9.60%
Total projected smart meter smart grid spend																														480,000,000
Reimbursements received from the DOE																														200,000,000
Noncurrent regulatory assets			510,000,000	524,000,000																																510,000,000
Upfront fee																																																							75
Recurring fee																																																							11
Gross transmission revenue requirement			9,000,000
Transmission revenue true up			5,000,000
Net transmission revenue requirement			14,000,000
Rate of return on common equity in federal energy regulatory committee complaint																								8.80%				8.70%
Customer refund liability			14,000,000																																	14,000,000															13,000,000
Regulatory liabilities			44,000,000	48,000,000																																44,000,000
Smart grid incremental cost			11,000,000
Site contingency, recovery from third party of environmental remediation cost																																1,000,000	5,000,000
Deferred costs, noncurrent																																			16,000,000			8,000,000
Rate cap imposed on public utility subsidiary			15.00%
Deferred purchased power costs																															306,000,000
Environmental costs recognized, recovery credited to expense			65,000,000	66,000,000
Baltimore Gas and Electric Company [Member] | OverRecoveredNaturalGasSupply [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities			7,000,000	11,000,000																																7,000,000
Baltimore Gas and Electric Company [Member] | FERC Transmission Complaint [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public utilities, approved return on equity, percentage																												10.80%
Baltimore Gas and Electric Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities			0	0																																0
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Electric Revenue [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities			7,000,000																																	7,000,000
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Gas Revenue [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities			12,000,000	9,000,000																																12,000,000
Baltimore Gas and Electric Company [Member] | Under-Recovered Electric Revenue Decoupling [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities				7,000,000
Baltimore Gas and Electric Company [Member] | Waldorf Project [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Capacity of natural gas fired combined cycle generation plant (in MW)																																		700
Initial term of proposed contract																																		20 years
Baltimore Gas and Electric Company [Member] | Under Recovered Electric Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory assets			10,000,000																																	10,000,000
Baltimore Gas and Electric Company [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory assets			15,000,000	4,000,000																																15,000,000
Noncurrent regulatory assets			4,000,000	3,000,000																																4,000,000
Baltimore Gas and Electric Company [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amortization period			P5Y
Noncurrent regulatory assets			159,000,000	148,000,000																																159,000,000
Baltimore Gas and Electric Company [Member] | Comprehensive Rate Order [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory assets																																			19,000,000
Baltimore Gas and Electric Company [Member] | Non-severance Merger Integration Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory assets																8,000,000
Increase (decrease) in regulatory asset																6,000,000
Baltimore Gas and Electric Company [Member] | Merger Integration Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory assets			4,000,000	3,000,000																																4,000,000
Noncurrent regulatory assets			6,000,000	9,000,000																																6,000,000
Baltimore Gas and Electric Company [Member] | Electric Generation Related Regulatory Asset [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory assets			28,000,000	37,000,000																																28,000,000
Noncurrent regulatory assets			20,000,000	30,000,000																																20,000,000
Baltimore Gas and Electric Company [Member] | Deferred Storm Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory assets																																																									16,000,000
Amortization period			P5Y																																5
Noncurrent regulatory assets			2,000,000	3,000,000																																2,000,000
Baltimore Gas and Electric Company [Member] | Transmission Rate Formula [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Net regulatory assets				1,000,000
Baltimore Gas and Electric Company [Member] | Severance Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory assets																20,000,000
Net regulatory assets																19,000,000
Baltimore Gas and Electric Company [Member] | Pension and Other Postretirement Benefits [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amortization period			P12Y
Baltimore Gas and Electric Company [Member] | Under Recovered Distribution Service Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			0	0																																0
Baltimore Gas and Electric Company [Member] | AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amortization period			P10Y
Noncurrent regulatory assets			128,000,000	66,000,000																																128,000,000
Baltimore Gas and Electric Company [Member] | Asset Retirement Obligations [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Noncurrent regulatory assets			16,000,000	10,000,000																																16,000,000
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Minimum purchase obligation																																																										25,000,000
Maximum purchase obligation																																																										35,000,000
License costs			39,000,000
Business Combination, Integration Related Costs																																				19,000,000
Commonwealth Edison and Baltimore Gas and Electric Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities			88,000,000																																	88,000,000
Scenario, Forecast [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenue reduction																																					$ (11,000,000)