Commitments and Contingencies - Schedule of Accruals for Environmental Matters (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	$ 315	$ 325
Accrual for Environmental Loss Contingencies, Gross	412	429
Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	0	0
Accrual for Environmental Loss Contingencies, Gross	67	72
Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	282	291
Accrual for Environmental Loss Contingencies, Gross	284	292
PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	31	31
Accrual for Environmental Loss Contingencies, Gross	32	33
Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	2	2
Accrual for Environmental Loss Contingencies, Gross	3	2
PEPCO Holdings Inc [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	0	1
Accrual for Environmental Loss Contingencies, Gross	26	30
Potomac Electric Power Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	0	0
Accrual for Environmental Loss Contingencies, Gross	23	27
Delmarva Power and Light Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	0	1
Accrual for Environmental Loss Contingencies, Gross	2	2
Atlantic City Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrued environmental liabilities	0	0
Accrual for Environmental Loss Contingencies, Gross	$ 1	$ 1