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Property, Plant and Equipment Property, Plant and Equipment- Narrative (Details) | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
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Electric—generation |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 5.37% | [1] | 4.36% | [1] | 5.94%
Electric—transmission and distribution |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 2.73% |  | 2.75% |  | 2.73%
Exelon Generation Co L L C [Member] | Electric—generation |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 5.37% |  | 4.36% |  | 5.94%
Commonwealth Edison Co [Member] | Electric—transmission and distribution |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 2.95% |  | 2.99% |  | 3.03%
Potomac Electric Power Company [Member] | Electric—transmission and distribution |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 2.40% |  | 2.35% |  | 2.17%
Atlantic City Electric Company [Member] | Electric—transmission and distribution |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 2.45% |  | 2.46% |  | 2.45%
[1] | See Note 8 — Early Plant Retirements for additional information on the accelerated net depreciation and amortization of Clinton, Quad Cities, Oyster Creek and TMI.

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