Variable Interest Entities - Narrative (Details)	3 Months Ended		6 Months Ended		9 Months Ended
	Jun. 30, 2016 USD ($) VIE	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) VIE	Jun. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) VIE	Jul. 31, 2014 USD ($)	Apr. 01, 2014 USD ($)
Variable Interest Entity [Line Items]
Other Commitment	$ 6,399,000,000		$ 6,399,000,000
Variable Interest Entity, Financial or Other Support, Amount			$ 13,000,000
Number of Variable Interest Entities not consolidated by equity holders | VIE	9		9			8
Number Of Variable Interest Entities Consolidated | VIE	9		9			7
Guarantor Obligations, Current Carrying Value	$ 75,000,000		$ 75,000,000
Guarantor Obligations, Maximum Exposure, Undiscounted	50,000,000		50,000,000
Payments for Restructuring			19,000,000
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		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		275,000,000
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Other Commitment	$ 5,589,000,000		$ 5,589,000,000				$ 91,000,000
Equity Method Investment, Ownership Percentage	50.01%		50.01%
Related Party Purchase Of Nuclear Output By Third Party Percentage			49.99%
Payments for Restructuring			$ 4,000,000
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
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	8,000,000		8,000,000
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Other Commitment	262,000,000		262,000,000
Payments for Restructuring			0
Baltimore Gas and Electric Company [Member] | RSB Bond Co LLC [Member]
Variable Interest Entity [Line Items]
Cash Remitted To VIE	21,000,000	$ 21,000,000	42,000,000	$ 42,000,000
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Other Commitment	9,000,000		9,000,000
Number Of Variable Interest Entities Consolidated | VIE						1
Due from Affiliates	1,000,000		1,000,000			$ 0
Guarantor Obligations, Maximum Exposure, Undiscounted	13,000,000		13,000,000
Payments for Restructuring			0
Atlantic City Electric Company [Member] | ATF [Member]
Variable Interest Entity [Line Items]
Cash Remitted To VIE	12,000,000	$ 14,000,000	26,000,000	$ 27,000,000
Constellation Energy Nuclear Group [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Due from Affiliates	308,000,000		308,000,000					$ 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		$ 637,000,000