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Property, Plant and Equipment Property, Plant and Equipment- Annual Depreciation Provisions as Percentage of Average Service Life (Details) | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | --- | ---
Electric—transmission and distribution |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 2.73% |  | 2.75% |  | 2.73%
Electric—generation |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 5.37% | [1] | 4.36% | [1] | 5.94%
Gas Distribution Equipment |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 2.07% |  | 2.10% |  | 2.17%
Common—electric and gas |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 6.98% |  | 7.05% |  | 7.41%
PECO Energy Co [Member] | Electric—transmission and distribution |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 2.35% |  | 2.37% |  | 2.32%
PECO Energy Co [Member] | Gas Distribution Equipment |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 1.90% |  | 1.89% |  | 1.82%
PECO Energy Co [Member] | Common—electric and gas |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 5.44% |  | 5.47% |  | 5.11%
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 2.61% |  | 2.58% |  | 2.56%
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 2.36% |  | 2.33% |  | 2.45%
Baltimore Gas and Electric Company [Member] | Common—electric and gas |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 8.50% |  | 8.64% |  | 9.45%
Pepco Holdings LLC [Member] | Electric—transmission and distribution |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 2.61% |  | 2.63% |  | 2.52%
Pepco Holdings LLC [Member] | Gas Distribution Equipment |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 1.59% |  | 2.07% |  | 2.57%
Pepco Holdings LLC [Member] | Common—electric and gas |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 6.30% |  | 6.50% |  | 8.12%
Delmarva Power & Light Company [Member] | Electric—transmission and distribution |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 2.77% |  | 2.75% |  | 2.49%
Delmarva Power & Light Company [Member] | Gas Distribution Equipment |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 1.59% |  | 2.07% |  | 2.57%
Delmarva Power & Light Company [Member] | Common—electric and gas |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |
Annual depreciation rate | 3.70% |  | 4.14% |  | 4.99%
[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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