Commitments and Contingencies - Narrative (Details)	3 Months Ended			12 Months Ended
	Dec. 31, 2016 USD ($) a MGPSite Open_claim MW	Sep. 30, 2016 USD ($)	Sep. 30, 2015 gal	Dec. 31, 2016 USD ($) a MGPSite Open_claim Customer MW	Dec. 31, 2015 USD ($)	Dec. 31, 1999 Principle_responsible_party	Dec. 31, 2014 USD ($)	May 30, 2012 USD ($)
Commitments and Contingencies [Line Items]
Power Volume | MW				220
Loss Contingency Accrual, Payments	$ 44,000,000
Litigation Settlement, Amount				$ (28,000,000)
Nuclear insurance liability limit per incident					$ 21,000,000
BusinessAcquisitionResidualcommitment | MW	55
Loss Contingency, Loss in Period	$ 50,000,000
Guarantee obligations maximum exposure	50,000,000			50,000,000
Asbestos liability reserve	83,000,000			83,000,000	95,000,000
Probable contingency (liability)	$ 22,000,000			$ 22,000,000
Open asbestos liability claims | Open_claim	230			230
Asbestos liability reserve related to anticipated claims	$ 61,000,000			$ 61,000,000
Rossville ash site [Member]
Commitments and Contingencies [Line Items]
Area of property | a	32			32
Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Loss Contingency Accrual	$ 0			$ 0
Loss Contingency, Damages Sought, Value				14,000,000
Nuclear financial protection pool value	450,000,000			450,000,000
Maximum recovery limit from a nuclear industry mutual insurance company in the event of multiple losses	13,000,000,000.0			13,000,000,000.0
Maximum annual assessment payment mandated by Price-Anderson Act for a nuclear incident	2,700,000,000			2,700,000,000
Total retrospective premium obligation under insurance from a nuclear industry mutual insurance company	353,000,000			353,000,000
Mutual Replacement Power Cost Insurance Maximum Retrospective Premium Obligation	3,200,000,000			3,200,000,000
Cost of spent nuclear fuel disposal per kWh of net nuclear generation	0.001			0.001
Net nuclear fuel disposal fees					49,000,000
Department of Energy SNF one-time fee applicable to nuclear generation	277,000,000			277,000,000
DOE SNF one-time fee with interest	1,024,000,000			$ 1,024,000,000
13-week Treasury Rate used to calculate DOE SNF one-time fee				0.355%
Environmental loss contingencies					$ 90,000,000
Total cost of remediation to be shared by PRPs				$ 90,000,000
Estimate of possible loss	$ 4,000,000			$ 4,000,000
Open asbestos liability claims | Open_claim	300			300
Costs Incurred, Development Costs				$ 454,000,000
Exelon Generation Co L L C [Member] | Minimum [Member]
Commitments and Contingencies [Line Items]
Total cost of remediation to be shared by PRPs	$ 225
Business Acquisition, Development Of New Generation Cost	450,000,000			$ 450,000,000
Business Acquisition, Expected New Generation Mwh | MW				285
Exelon Generation Co L L C [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Total cost of remediation to be shared by PRPs	650
Business Acquisition, Development Of New Generation Cost	500,000,000			$ 500,000,000
Business Acquisition, Expected New Generation Mwh | MW				300
Exelon Generation Co L L C [Member] | Equity Method Investments [Member]
Commitments and Contingencies [Line Items]
Purchase obligations, due within two years	5,000,000			$ 5,000,000
Unrecorded Unconditional Purchase Obligation	39,000,000			39,000,000
Unrecorded unconditional purchase obligation, due in next 12 months	34,000,000			34,000,000
Other unrecorded amounts	20,000,000			20,000,000
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Nuclear insurance liability limit per incident	13,400,000,000.0			13,400,000,000.0
Exelon Generation Co L L C [Member] | Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Mutual Property Insurance Distribution To Members	$ 21,000,000			$ 21,000,000			$ 18,000,000
Commonwealth Edison Co [Member]
Commitments and Contingencies [Line Items]
Total number of MGP sites | MGPSite	42			42
Sites approved for clean-up | MGPSite	18			18
Sites under study/remediation | MGPSite	24			24
Increase (decrease) in accrual for environmental loss contingencies		$ 7,000,000
Minimum number of customers ComEd can be held liable to for power interruption | Customer				30,000
PECO Energy Co [Member]
Commitments and Contingencies [Line Items]
Total number of MGP sites | MGPSite	26			26
Sites approved for clean-up | MGPSite	17			17
Sites under study/remediation | MGPSite	9			9
Increase (decrease) in accrual for environmental loss contingencies		0
Baltimore Gas and Electric Company [Member]
Commitments and Contingencies [Line Items]
Litigation Settlement, Amount				$ (28,000,000)
Total number of MGP sites | MGPSite	13			13
Sites under study/remediation | MGPSite	2			2
Number of parties jointly and severally liable In environmental protection agency action | Principle_responsible_party						19
Baltimore Gas and Electric Company [Member] | Deferrable Interest Subordinated Debentures [Member]
Commitments and Contingencies [Line Items]
Interest rate on long-term debt	6.20%			6.20%
Baltimore Gas and Electric Company [Member] | Minimum [Member]
Commitments and Contingencies [Line Items]
Estimate of possible loss	$ 50,000,000			$ 50,000,000
Baltimore Gas and Electric Company [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Estimate of possible loss	64,000,000			64,000,000				$ 1,700,000
Calpine Corporation [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Estimate of possible loss	$ 10,000,000			10,000,000
Pepco Holdings LLC [Member]
Commitments and Contingencies [Line Items]
Litigation Settlement, Amount				$ 1,600,000
Number of Real Estate Properties | MGPSite	9			9
Pepco Holdings LLC [Member] | Minimum [Member]
Commitments and Contingencies [Line Items]
Estimate of possible loss	$ 7,000,000			$ 7,000,000
Pepco Holdings LLC [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Estimate of possible loss	$ 18,000,000			18,000,000
Potomac Electric Power Company [Member]
Commitments and Contingencies [Line Items]
Guarantee obligations maximum exposure		14,000,000
QuantityOfMineralOilSPill | gal			6,100
Quantity of Mineral Oil Spill Recovered			80.00%
Potomac Electric Power Company [Member] | Minimum [Member]
Commitments and Contingencies [Line Items]
Environmental Exit Costs, Anticipated Cost				3,000,000
Potomac Electric Power Company [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Environmental Exit Costs, Anticipated Cost				$ 6,000,000
Delmarva Power and Light Company [Member]
Commitments and Contingencies [Line Items]
Total number of MGP sites | MGPSite	2			2
Guarantee obligations maximum exposure		17,000,000
Atlantic City Electric Company [Member]
Commitments and Contingencies [Line Items]
Guarantee obligations maximum exposure		$ 13,000,000
Merger Commitment [Member]
Commitments and Contingencies [Line Items]
Investments	$ 0			$ 0
Merger Commitment [Member] | Minimum [Member]
Commitments and Contingencies [Line Items]
Investments	0			0
Merger Commitment [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Investments	$ 0			$ 0