Variable Interest Entities - Narrative (Details)	3 Months Ended			9 Months Ended
	Mar. 31, 2016 USD ($) VIE	Dec. 31, 2015 USD ($) VIE	Mar. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jul. 31, 2014 USD ($)	Apr. 01, 2014 USD ($)
Variable Interest Entity [Line Items]
Other Commitment	$ 6,282,000,000
Variable Interest Entity, Financial or Other Support, Amount	$ 14,000,000
Number of Variable Interest Entities not consolidated by equity holders | VIE	9	8
Number Of Variable Interest Entities Consolidated | VIE	9	7
Guarantor Obligations, Current Carrying Value	$ 75,000,000
Guarantor Obligations, Maximum Exposure, Undiscounted	53,000,000
Payments for Restructuring	(4,000,000)
Note Receivable				$ 27,000,000
Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests	250,000,000	$ 172,000,000
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value	275,000,000
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Other Commitment	$ 5,468,000,000				$ 91,000,000
Equity Method Investment, Ownership Percentage	50.01%
Related Party Transaction Required Purchase Of Power Percentage	85.00%
Related Party Purchase Of Nuclear Output By Third Party Percentage	49.99%
Payments for Restructuring	$ (3,000,000)
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
Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests		78,000,000
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value	7,000,000
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Other Commitment	262,000,000
Baltimore Gas and Electric Company [Member] | RSB Bond Co LLC [Member]
Variable Interest Entity [Line Items]
Cash Remitted To VIE	20,000,000	$ 21,000,000
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Other Commitment	8,000,000
Number Of Variable Interest Entities Consolidated | VIE		1
Guarantor Obligations, Maximum Exposure, Undiscounted	14,000,000
Payments for Restructuring	0
Atlantic City Electric Company [Member] | ATF [Member]
Variable Interest Entity [Line Items]
Cash Remitted To VIE	14,000,000		$ 13,000,000
Constellation Energy Nuclear Group [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Due from Affiliates	304,000,000					$ 400,000,000
Severance Benefits Obligations Balance						6,000,000
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
Equity Method Investment Variable Interest Entities [Member] | Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value	$ 637,000,000