Debt and Credit Agreements - Schedule of Issuance of Long-Term Debt (Details) - USD ($) $ in Millions	Jun. 30, 2016	Jun. 30, 2015
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 750
SeniorUnsecured245April2021 [Member]
Debt Instrument [Line Items]
Interest Rate	2.45%
Debt Instrument, Face Amount	$ 300
SeniorUnsecured340April2026 [Member]
Debt Instrument [Line Items]
Interest Rate	3.40%
Debt Instrument, Face Amount	$ 750
SeniorUnsecured445April2046 [Member]
Debt Instrument [Line Items]
Interest Rate	4.45%
Debt Instrument, Face Amount	$ 750
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 10
Exelon Generation Co L L C [Member] | Energy Efficiency Project Financing [Member]
Debt Instrument [Line Items]
Interest Rate	1.43%
Debt Instrument, Face Amount	$ 63
Exelon Generation Co L L C [Member] | EscoNotes390February2018 [Member]
Debt Instrument [Line Items]
Interest Rate	3.90%
Debt Instrument, Face Amount	$ 7
Exelon Generation Co L L C [Member] | DominionFederal [Member]
Debt Instrument [Line Items]
Interest Rate	0.00%
Debt Instrument, Face Amount	$ 16
Exelon Generation Co L L C [Member] | DOE Financing Project [Member] | Energy Efficiency Project Financing [Member]
Debt Instrument [Line Items]
Interest Rate	4.11%
Debt Instrument, Face Amount	$ 150
Commonwealth Edison Co [Member] | FirstMortgageBonds120 [Member]
Debt Instrument [Line Items]
Interest Rate	2.55%
Debt Instrument, Face Amount	$ 500
Commonwealth Edison Co [Member] | FirstMortgageBonds121 [Member]
Debt Instrument [Line Items]
Interest Rate	3.65%
Debt Instrument, Face Amount	$ 700
Potomac Electric Power Company [Member] | EscoNotes330August2017 [Member]
Debt Instrument [Line Items]
Interest Rate	3.30%
Debt Instrument, Face Amount	$ 1