Regulatory Matters Regulatory Matters - Estimated Commitments related to PJM Agreements (Details) $ in Millions	Dec. 31, 2017 USD ($)
Other Commitments [Line Items]
Total	$ 137
Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Total	164
2018	36
2019	60
2020	44
2021	24
2022	0
PECO Energy Co [Member]
Other Commitments [Line Items]
Total	53
2018	16
2019	19
2020	10
2021	5
2022	3
Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Total	118
2018	35
2019	35
2020	35
2021	13
2022	0
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Total	86
2018	5
2019	11
2020	27
2021	33
2022	10
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Total	27
2018	19
2019	2
2020	1
2021	2
2022	3
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Total	121
2018	68
2019	20
2020	6
2021	21
2022	$ 6