Variable Interest Entities - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) VIE	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) VIE	Sep. 30, 2014 USD ($)	Jun. 09, 2015 USD ($)	Dec. 31, 2014 USD ($) VIE	Aug. 18, 2014	Jul. 18, 2014 USD ($)	Apr. 01, 2014 USD ($)	Mar. 31, 2014
Variable Interest Entity [Line Items]
Number of Variable Interest Entities not consolidated by equity holders | VIE	8		8			6
Number Of Variable Interest Entities Consolidated | VIE	7		7			6
Guarantor Obligations, Current Carrying Value	$ 75,000,000		$ 75,000,000
Guarantor Obligations, Maximum Exposure, Undiscounted	9,958,000,000		9,958,000,000
Note Receivable			$ 27,000,000
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Equity Method Investment, Ownership Percentage							67.00%			50.01%
Related Party Transaction Required Purchase Of Power Percentage			85.00%
Guarantor Obligations, Current Carrying Value	11,000,000		$ 11,000,000
Related Party Purchase Of Nuclear Output By Third Party Percentage			49.99%
Payables to affiliates	106,000,000		$ 106,000,000			$ 107,000,000
Guarantor Obligations, Maximum Exposure, Undiscounted	7,227,000,000		7,227,000,000
Exelon Generation Co L L C [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value	275,000,000		275,000,000
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value					$ 275,000,000				$ 7,000,000
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value	637,000,000		637,000,000
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	264,000,000		264,000,000
Baltimore Gas and Electric Company [Member] | RSB Bond Co LLC [Member]
Variable Interest Entity [Line Items]
Remittance of payments received from customers for rate stabilization to BondCo.	21,000,000	$ 21,000,000	63,000,000	$ 63,000,000
Constellation Energy Nuclear Group [Member]
Variable Interest Entity [Line Items]
Severance Benefits Obligations Balance									6,000,000
Severance Costs			1,000,000
Constellation Energy Nuclear Group [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Due from Affiliates	296,000,000		296,000,000						400,000,000
Distributed Energy Company [Member]
Variable Interest Entity [Line Items]
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests	$ 250,000,000		$ 250,000,000					$ 91,000,000
Financial Guarantee [Member] | Constellation Energy Nuclear Group [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted									165,000,000
Payment Guarantee [Member] | Constellation Energy Nuclear Group [Member]
Variable Interest Entity [Line Items]
Payables to affiliates									$ 245,000,000