Jointly Owned Electric Utility Plant - Ownership Interests in Jointly Owned Electric Plants and Transmission Facilities (Details) $ in Millions		12 Months Ended
		Dec. 31, 2018 USD ($) V mi	Dec. 31, 2017 USD ($)
Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Miles of transmission voltage lines | mi		127
Transmission line capacity | V		500
Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Miles of transmission voltage lines | mi		151.3
Transmission line capacity | V		500
Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Transmission line capacity | V		500
Substation capacity | V		500
Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Miles of transmission voltage lines | mi		2.5
Transmission line capacity | V		500
New Freedom Switching [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Transmission line capacity | V		500
Electric Transmission [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Plant	[1],[2]	$ 28	$ 27
Accumulated depreciation	[1],[2]	16	15
Construction work in progress	[2]	1	0
Electric Transmission [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Plant	[1],[3]	103	102
Accumulated depreciation	[1],[3]	53	52
Construction work in progress	[3]	0	0
Other Service [Member] | Other Locations [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Plant	[1],[4]	15	15
Accumulated depreciation	[1],[4]	13	13
Construction work in progress	[4]	$ 0	0
Exelon Generation Co L L C [Member] | Merrill Creek [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		44.24%
Exelon Generation Co L L C [Member] | Nuclear Plant [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		42.59%
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Quad Cities [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		75.00%
Plant	[1]	$ 1,131	1,074
Accumulated depreciation	[1]	587	550
Construction work in progress		$ 13	35
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Peach Bottom [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		50.00%
Plant	[1]	$ 1,451	1,417
Accumulated depreciation	[1]	523	461
Construction work in progress		$ 15	18
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	[5]	42.59%
Plant	[1],[5]	$ 648	631
Accumulated depreciation	[1],[5]	227	205
Construction work in progress	[5]	$ 44	33
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Nine Mile Point [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		82.00%
Plant	[1]	$ 910	839
Accumulated depreciation	[1]	126	97
Construction work in progress		56	55
Exelon Generation Co L L C [Member] | Fossil Fuel Generation [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Plant		$ 3
Exelon Generation Co L L C [Member] | Fossil Fuel Generation [Member] | Wyman [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		5.89%
Plant	[1]	$ 4	3
Accumulated depreciation	[1]	3	3
Construction work in progress		$ 0	$ 0
PECO Energy Co [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		22.00%
PECO Energy Co [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		42.55%
PECO Energy Co [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		20.72%
PECO Energy Co [Member] | Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		42.55%
Baltimore Gas and Electric Company [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		7.00%
Baltimore Gas and Electric Company [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		10.56%
Potomac Electric Power Company [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		27.00%
Potomac Electric Power Company [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		9.72%
Potomac Electric Power Company [Member] | Valley Forge [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		11.90%
Delmarva Power & Light Company [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		9.00%
Delmarva Power & Light Company [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		1.00%
Delmarva Power & Light Company [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		3.72%
Delmarva Power & Light Company [Member] | Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		7.45%
Delmarva Power & Light Company [Member] | Merrill Creek [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		11.91%
Delmarva Power & Light Company [Member] | Valley Forge [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		7.40%
Atlantic City Electric Company [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		8.00%
Atlantic City Electric Company [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		13.90%
Atlantic City Electric Company [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		3.83%
Atlantic City Electric Company [Member] | Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		7.45%
Atlantic City Electric Company [Member] | Merrill Creek [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		4.83%
Atlantic City Electric Company [Member] | Valley Forge [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		6.60%
Atlantic City Electric Company [Member] | New Freedom Switching [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		21.78%

[1] Excludes asset retirement costs and general plant.

[2] PECO, BGE, Pepco, DPL and ACE own a 22%, 7%, 27%, 9% and 8% share, respectively, in 127 miles of 500kV lines located in Pennsylvania as well as a 20.72%, 10.56%, 9.72%, 3.72% and 3.83% share, respectively, of a 500kV substation immediately outside of the Conemaugh fossil-generating station which supplies power to the 500kV lines including, but not limited to, the lines noted above.

[3] PECO, DPL and ACE own a 42.55%, 1% and 13.9% share, respectively in 151.3 miles of 500kV lines located in New Jersey and of the Salem generating plant substation. PECO, DPL and ACE also own a 42.55%, 7.45% and 7.45% share, respectively, in 2.5 miles of 500kV line located over the Delaware River. ACE also has a 21.78% share in a 500kV New Freedom Switching

[4] Generation, DPL and ACE own a 44.24%, 11.91% and 4.83% share, respectively in assets located at Merrill Creek Reservoir located in New Jersey. Pepco, DPL and ACE own a 11.9%, 7.4% and 6.6% share, respectively, in Valley Forge Corporate Center.

[5] Generation also owns a proportionate share in the fossil-fuel combustion turbine at Salem, which is fully depreciated. The gross book value was $3 million at December 31, 2018 and 2017.