Commitments and Contingencies - Schedule of Accruals for Environmental Matters (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	$ 376	$ 347
Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	309	277
Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	63	63
Exelon Generation Co L L C [Member] | Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	0	0
Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	269	238
Other Increase (Decrease) in Environmental Liabilities	50
Commonwealth Edison Co [Member] | Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	268	235
PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	41	45
Other Increase (Decrease) in Environmental Liabilities	1
PECO Energy Co [Member] | Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	39	42
Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	3	1
Baltimore Gas and Electric Company [Member] | Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	$ 2	$ 0