Commitments and Contingencies Commitments and Contingencies - Narrative (Details)					3 Months Ended			12 Months Ended
		Nov. 04, 2016	Nov. 01, 2015 USD ($)	Sep. 23, 2015 USD ($)	Dec. 31, 2018 USD ($) employee Open_claim MGPSite	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($) MW	Dec. 31, 2018 USD ($) employee Open_claim MGPSite MW	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Feb. 17, 2012 USD ($)
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[1],[2]				$ 1,378,000,000			$ 1,378,000,000
Direct Investment Commitment											$ 1,000,000,000
Power Volume | MW							10	220
Business Acquisition Residual Commitment | MW							55
Loss Contingency, Loss in Period										$ 50,000,000
Nontrade Receivables, Current	[3]				124,000,000		$ 94,000,000	$ 124,000,000	94,000,000
Nontrade Receivables, Noncurrent	[4]				15,000,000		15,000,000	15,000,000	15,000,000
Accounts Payable, Other, Current	[3],[5]				(17,000,000)		(11,000,000)	(17,000,000)	(11,000,000)
DOE Spent Nuclear Fuel One Time Fee					34,000,000			34,000,000
Operating Expenses	[6]							32,143,000,000	29,619,000,000	28,106,000,000
Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[1],[2]				763,000,000			763,000,000
Direct Investment Commitment
Entity Number of Employees | employee					1,500			1,500
Leasehold Improvements, Gross					$ 90,000,000			$ 90,000,000
Lessee, Operating Lease, Term of Contract		20 years
Costs Incurred, Development Costs								458,000,000
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					13,600,000,000			13,600,000,000
Maximum annual assessment payment mandated by Price-Anderson Act for a nuclear incident					3,100,000,000			3,100,000,000
Mutual Insurance Total Retrospective Premium Obligation					345,000,000			345,000,000
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
Spent Nuclear Fuel Storage Reimbursement	[7]							1,274,000,000
Spent Nuclear Fuel Storage Reimbursement Net Co Owners	[7],[8]							1,100,000,000
DOE Spent Nuclear Fuel One Time Fee					277,000,000			277,000,000
DOE Spent Nuclear Fuel One Time Fee With Interest					1,171,000,000		1,147,000,000	$ 1,171,000,000	1,147,000,000
Spent Nuclear Fuel Treasury Interest Rate								2.351%
Loss Contingency Accrual, Provision					20,000,000
Environmental loss contingencies							90,000,000		90,000,000
Asbestos Liability Reserve					$ 79,000,000		78,000,000	$ 79,000,000	78,000,000
Open Asbestos Liability Claims | Open_claim					238			238
Exelon Generation Co L L C [Member] | Minimum [Member]
Commitments and Contingencies [Line Items]
Direct Investment Commitment					$ 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]
Direct Investment Commitment					500,000,000			$ 500,000,000
Business Acquisition, Expected New Generation Mwh | MW								300
Exelon Generation Co L L C [Member] | West Lake [Member]
Commitments and Contingencies [Line Items]
Loss Contingency Accrual, Provision					280,000,000
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Nuclear insurance liability limit per incident					14,100,000,000			$ 14,100,000,000
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Nuclear financial protection pool value						$ 454,000,000
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					58,000,000		60,000,000	58,000,000	60,000,000	$ 21,000,000
Commonwealth Edison Co [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[2],[9]				23,000,000			23,000,000
Direct Investment Commitment
Total number of MGP sites | MGPSite					42			42
Sites approved for clean-up | MGPSite					21			21
Sites under study/remediation | MGPSite					21			21
Other Increase (Decrease) in Environmental Liabilities						$ 48,000,000
PECO Energy Co [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[2],[9]				$ 25,000,000			$ 25,000,000
Direct Investment Commitment
Total number of MGP sites | MGPSite					26			26
Sites approved for clean-up | MGPSite					17			17
Sites under study/remediation | MGPSite					9			9
Baltimore Gas and Electric Company [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[2],[9],[10],[11]				$ 143,000,000			$ 143,000,000
Direct Investment Commitment
Total number of MGP sites | MGPSite					13			13
Sites approved for clean-up | MGPSite					9			9
Sites under study/remediation | MGPSite					4			4
Common Equity Tier One Capital Ratio					48.00%			48.00%
Occupancy, Net			$ 42,000,000	$ 12,000,000
Operating Leases, Income Statement, Initial Direct Costs							25,000,000
Oil and Gas Property, Lease Operating Expense							29,000,000
Operating Expenses							28,000,000
Pepco Holdings LLC [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[2]				$ 377,000,000			$ 377,000,000
Direct Investment Commitment
Potomac Electric Power Company [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[2]				86,000,000			86,000,000
Direct Investment Commitment
Accrued Liabilities and Other Liabilities					30,000,000		28,000,000	30,000,000	28,000,000
Delmarva Power & Light Company [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[2],[9]				96,000,000			96,000,000
Direct Investment Commitment
Total number of MGP sites | MGPSite					3			3
Sites approved for clean-up | MGPSite					2			2
Common Equity Tier One Capital Ratio					48.00%			48.00%
Atlantic City Electric Company [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[2]				$ 32,000,000			$ 32,000,000
Direct Investment Commitment
Common Equity Tier One Capital Ratio					30.00%			30.00%
Open Claims [Member] | Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Asbestos Liability Reserve					$ 24,000,000			$ 24,000,000
Estimated Future Claims [Member] | Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Asbestos Liability Reserve					$ 55,000,000			$ 55,000,000

[1] )Excludes Generation’s contingent operating lease payments associated with contracted generation agreement

[2] )Includes amounts related to shared use land arrangement

[3] )Recorded in Accounts receivable, other.

[4] )Recorded in Deferred debits and other assets, oth

[5] )Non-CENG amounts owed to co-owners are recorded in Accounts receivable, other. CENG amounts owed to co-owners are recorded in Accounts payable. Represents amounts owed to the co-owners of Peach Bottom, Quad Cities, and Nine Mile Point Unit 2 generating facilities

[6] Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 23 — Supplemental Financial Information for additional information on total utility taxes.

[7] )Includes $53 and $49, respectively, for amounts received since April 1, 2014, for costs incurred under the CENG DOE Settlement Agreements prior to the consolidation of CEN

[8] )Total after considering amounts due to co-owners of certain nuclear stations and to the former owner of Oyster Cree

[9] )Amounts related to certain real estate leases and railroad licenses effectively have indefinite payment periods. As a result, ComEd, PECO, BGE and DPL have excluded these payments from the remaining years as such amounts would not be meaningful. ComEd's, PECO’s, BGE’s and DPL's average annual obligation for these arrangements, included in each of the years 2019 - 2023, was $3 million, $5 million, $1 million and $1 million respectivel

[10] )The BGE column above includes minimum future lease payments associated with a 6-year lease for the Baltimore City conduit system that became effective during the fourth quarter of 2016. BGE's total commitments under the lease agreement are $26 million, $28 million, $28 million and $14 million related to years 2019 - 2022 , respectivel

[11] )The BGE column above includes minimum future lease payments associated with a 6-year lease for the Baltimore City conduit system that became effective during the fourth quarter of 2016. BGE's total commitments under the lease agreement are $26 million, $28 million, $28 million and $14 million related to years 2019 - 2022 , respectivel