Commitments and Contingencies - Schedule of Accruals for Environmental Matters (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	$ 337	$ 347
Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	63	63
Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	227	238
PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	44	45
Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	3	1
Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	267	277
Accrual For MGP Investigation And Remediation [Member] | Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	0	0
Accrual For MGP Investigation And Remediation [Member] | Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	224	235
Accrual For MGP Investigation And Remediation [Member] | PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	41	42
Accrual For MGP Investigation And Remediation [Member] | Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	$ 2	$ 0