Regulatory Matters - Narrative (Details)																							1 Months Ended			12 Months Ended					20 Months Ended	60 Months Ended	65 Months Ended
	Dec. 17, 2015 USD ($)	Nov. 30, 2015 MWh	Nov. 06, 2015 USD ($)	Oct. 20, 2015	Sep. 10, 2015 USD ($)	Jun. 19, 2015 MWh	May. 27, 2015 USD ($)	May. 07, 2015 USD ($)	Mar. 27, 2015 USD ($)	Dec. 08, 2014	Sep. 15, 2014 USD ($)	Aug. 21, 2014 USD ($)	Dec. 13, 2013	Dec. 02, 2013 V mi	Aug. 23, 2013 USD ($)	Mar. 15, 2013 USD ($)	Feb. 27, 2013	Dec. 05, 2012 USD ($)	Nov. 01, 2012 MWh	Jul. 31, 2012 USD ($)	Apr. 12, 2012 MW	Aug. 09, 2011 USD ($)	Jan. 31, 2014 USD ($)	Sep. 30, 2012 USD ($)	Aug. 31, 2010 USD ($) smart_meter	Dec. 31, 2015 USD ($) V smart_meter	Dec. 31, 2014 USD ($) MW	Dec. 31, 2013 USD ($)	Dec. 31, 2012	Dec. 31, 2007 USD ($)	Dec. 31, 2015 USD ($) smart_meter	Nov. 30, 2010 USD ($)	Nov. 30, 2005 USD ($)	Nov. 05, 2015 USD ($)	Oct. 30, 2015 USD ($)	Jun. 03, 2014 USD ($)	Mar. 31, 2014 USD ($)	Feb. 26, 2014 USD ($)	Mar. 31, 2012 USD ($)	Dec. 16, 2010 USD ($)
Regulatory Matters Additional Narrative Information [Line Items]
Revenue reduction																							$ 8,000,000
Substation kilovolt | V																										500,000
Near zero emissions coal fueled generation plant | MW																											166
Parent company pension OPEB regulatory assets noncurrent																										$ 3,156,000,000					$ 3,156,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount																										$ (50,000,000)	$ 269,000,000	$ 353,000,000
Public Utilities, Approved Equity Capital Structure, Annual Reconciliation, Percentage																										7.02%	7.04%	6.94%
Regulatory Assets																										$ 6,824,000,000	$ 6,923,000,000				6,824,000,000
Noncurrent regulatory assets																										6,065,000,000	6,076,000,000				6,065,000,000
Regulatory liabilities																										369,000,000	310,000,000				369,000,000
Business Combination, Integration Related Costs																										80,000,000	179,000,000				121,000,000
Regulatory Liabilities																										4,570,000,000	4,860,000,000				4,570,000,000
Public Utilities, Approved Rate Increase (Decrease), Annual Reconciliation, Amount																										(152,000,000)	72,000,000	$ 181,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount																										$ (67,000,000)	$ 232,000,000	$ 341,000,000
Public Utilities, Approved Equity Capital Structure, Initial Revenue Requirement, Percentage																										7.05%	7.06%	6.94%
Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										$ 92,000,000	$ 59,000,000				92,000,000
Over Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										131,000,000	84,000,000				$ 131,000,000
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Additional revenue requirement allowed by updated government order																										$ 137,000,000	$ 88,000,000
Weighted average debt and equity return																										8.61%	8.62%	8.70%			8.61%
Rate of return on common equity																										11.50%	11.50%	11.50%
Subsequent contribution to technology innovation trust																				$ 4,000,000
Utility annual customer assistance																				$ 10,000,000
Term of contract																										20 years
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%
Regulatory Assets																										$ 1,113,000,000	$ 1,201,000,000				$ 1,113,000,000
Noncurrent regulatory assets																										895,000,000	852,000,000				895,000,000
Gross transmission revenue requirement																										68,000,000	36,000,000	$ 38,000,000
Transmission revenue true up																										18,000,000	(14,000,000)	30,000,000
Net transmission revenue requirement																										86,000,000	22,000,000	$ 68,000,000
Regulatory liabilities																										155,000,000	125,000,000				155,000,000
Business Combination, Integration Related Costs																										10,000,000	4,000,000
Regulatory Liabilities																										3,614,000,000	3,780,000,000				3,614,000,000
Customer refundable fees																										$ 0	3,000,000				0
Customer refundable fees, interest																											1,000,000
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																										$ 52,000,000	25,000,000				52,000,000
Commonwealth Edison Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										53,000,000	19,000,000				$ 53,000,000
Over Recovered electric Supply Costs																										29,000,000	3,000,000
Renewable Energy Requirement Revenue																										$ 24,000,000	$ 16,000,000
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 | mi														60
Substation kilovolt | V														345,000
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Low income sector consumption reduction targets Act 129 Phase II																		4.50%
Electric distribution tax repairs																						$ 171,000,000
Gas distribution tax repairs refund																								$ 54,000,000
Smart meters initial phase deployment | smart_meter																										1,600,000.0					1,600,000.0
Estimated number of smart meters to be installed | smart_meter																										1,700,000					1,700,000
Projected investment in smart meters																										$ 589,000,000					$ 589,000,000
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																										578,000,000					578,000,000
Total smart grid spend on investment																										155,000,000					155,000,000
Smart grid investment grant awarded							$ 275,000,000	$ 534,000,000
Cumulative consumption reduction targets | MWh						2,080,553													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
Requested increase in electric revenues																																								$ 225,000,000
Requested increase in gas revenues																																								$ 20,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount					$ 127,000,000				$ 190,000,000
Public Utilities, Requested Rate Increase (Decrease), Percentage									10.95%
Regulatory Assets																										1,617,000,000	$ 1,558,000,000				1,617,000,000
Noncurrent regulatory assets																										1,583,000,000	1,529,000,000				1,583,000,000
Regulatory liabilities																										112,000,000	90,000,000				112,000,000
Cost recovery for significant one-time events	$ 7,000,000
Business Combination, Integration Related Costs																										5,000,000	2,000,000
Regulatory Liabilities																										639,000,000	747,000,000				639,000,000
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%
Cumulative consumption reduction targets | MWh		2,100,875
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																										40,000,000	34,000,000				40,000,000
PECO Energy Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										60,000,000	$ 58,000,000				$ 60,000,000
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Current year revenue adjustment																										$ 200,000,000
Weighted average debt and equity return																										8.46%	8.53%	8.35%			8.46%
Rate of return on common equity																										11.30%	11.30%	11.30%
Increase in electric delivery service revenue resulting from rate case settlement or order.																											$ 22,000,000	$ 34,000,000
Increase in gas delivery service revenue resulting from rate case settlement or order.																											38,000,000	12,000,000
Estimated number of smart meters to be installed | smart_meter																									2,000,000
Projected investment in smart meters			$ 103,000,000																							$ 37,000,000					$ 37,000,000
Total smart meter spend on investment			140,000,000
Vendor refund			30,000,000
Annual depreciation expense decrease regulated property												$ 20,000,000
Adjustment to electric revenues increase requested			$ 121,000,000								$ 99,000,000				$ 83,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount											$ 68,000,000				$ 24,000,000											79,000,000
Requested rate of return on common equity			10.60%										9.75%
Rate Of Return Common Equity Gas Distribution			10.50%										9.60%
Regulatory Assets																										781,000,000	724,000,000				781,000,000
Total projected smart meter smart grid spend																									$ 480,000,000
Reimbursements received from the DOE																									$ 200,000,000
Noncurrent regulatory assets																										514,000,000	510,000,000				514,000,000
Upfront fee																																						$ 75
Recurring fee																																		$ 5.5				$ 11
Gross transmission revenue requirement																										0	9,000,000	2,000,000
Transmission revenue true up																										(3,000,000)	5,000,000	(3,000,000)
Net transmission revenue requirement																										(3,000,000)	14,000,000	$ (1,000,000)
Rate of return on common equity in federal energy regulatory committee complaint										8.80%							8.70%
Regulatory liabilities																										38,000,000	44,000,000				38,000,000
Smart grid incremental cost																										11,000,000
Business Combination, Integration Related Costs																										5,000,000	2,000,000
Site contingency, recovery from third party of environmental remediation cost																																$ 1,000,000	$ 5,000,000
Regulatory Liabilities																										$ 222,000,000	244,000,000				222,000,000
Deferred costs, noncurrent																																					$ 8,000,000		$ 16,000,000
Rate cap imposed on public utility subsidiary																										15.00%
Deferred purchased power costs																														$ 306,000,000
Environmental costs recognized, recovery credited to expense																										$ 73,000,000	65,000,000
Baltimore Gas and Electric Company [Member] | FERC Transmission Complaint [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Approved Return on Equity, Percentage				10.00%													10.80%
Customer refund liability																																			$ 14,000,000
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 Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																										19,000,000	28,000,000				19,000,000
Regulatory Liabilities																										18,000,000	7,000,000				18,000,000
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Gas Revenue [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										1,000,000	12,000,000				1,000,000
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Electric Revenue [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																											7,000,000
Baltimore Gas and Electric Company [Member] | Under-Recovered Electric Revenue Decoupling [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																										30,000,000					30,000,000
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) | MW																					700
Initial term of proposed contract																					20 years
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
Business Combination, Integration Related Costs																										25,000,000	11,000,000
Exelon Generation Co L L C [Member] | Conowingo [Member]
Regulatory Matters Additional Narrative Information [Line Items]
License costs																										23,000,000
Exelon Generation Co L L C [Member] | Muddy Run [Member]
Regulatory Matters Additional Narrative Information [Line Items]
License costs																										22,000,000
Commonwealth Edison and Baltimore Gas and Electric Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities																										94,000,000					94,000,000
Energy Efficiency And Demand Response Programs [Member] | PECO Energy Co [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Cumulative consumption reduction targets | MWh		1,962,659
Over-Recovered Electric Transmission Cost [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										3,000,000	3,000,000				3,000,000
Over Recovered Electric Energy And Transmission Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										14,000,000					14,000,000
DSP Program costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										35,000,000	39,000,000				35,000,000
OverRecoveredNaturalGasSupply [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										22,000,000	16,000,000				22,000,000
OverRecoveredNaturalGasSupply [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																										5,000,000	$ 7,000,000				5,000,000
Stride Program [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Captial and OM estimates current year																										113,000,000					113,000,000
Regulatory liabilities																										$ 1,000,000					$ 1,000,000