Regulatory Matters - Estimated Commitments related to PJM Agreements (Details) - USD ($) $ in Millions	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016
Other Commitments [Line Items]
Total	$ 513	$ 137
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Total			$ 444
Pepco Holdings LLC [Member] | Successor [Member]
Other Commitments [Line Items]
Total	323
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Total	126
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Total	86
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Total	111
Construction Expansion Plans [Member] | Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Total	97
2015	64
2016	28
2017	5
2018	0
2019	0
Construction Expansion Plans [Member] | PECO Energy Co [Member]
Other Commitments [Line Items]
Total	34
2015	14
2016	10
2017	7
2018	2
2019	1
Construction Expansion Plans [Member] | Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Total	226
2015	113
2016	55
2017	44
2018	14
2019	0
Construction Expansion Plans [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Total	104
2015	6
2016	39
2017	40
2018	19
2019	0
Construction Expansion Plans [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Total	63
2015	47
2016	16
2017	0
2018	0
2019	0
Construction Expansion Plans [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Total	93
2015	36
2016	39
2017	18
2018	0
2019	$ 0