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Regulatory Matters Regulatory Matters - Capitalized Ratemaking Amounts Not Recognized (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
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Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes |  | $ 65 | $ 69
Commonwealth Edison Co [Member] |  |  |
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes | [1] | 8 | 6
PECO Energy Co [Member] |  |  |
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes |  | 0 | 0
Baltimore Gas and Electric Company [Member] |  |  |
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes | [2] | 49 | 53
Pepco Holdings LLC [Member] |  |  |
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes |  | 8 | 10
Potomac Electric Power Company [Member] |  |  |
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes | [3] | 5 | 6
Delmarva Power & Light Company [Member] |  |  |
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes | [3] | 3 | 4
Atlantic City Electric Company [Member] |  |  |
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes |  | $ 0 | $ 0
[1] | Reflects ComEd's unrecognized equity returns earned for ratemaking purposes on its electric distribution formula rate regulatory assets.
[2] | BGE's authorized amounts capitalized for ratemaking purposes primarily relate to earnings on shareholders' investment on its AMI programs
[3] | Pepco's and DPL's authorized amounts capitalized for ratemaking purposes relate to earnings on shareholders' investment on their respective AMI Programs and Energy Efficiency and Demand Response Programs. The earnings on energy efficiency are on Pepco DC and DPL DE programs only.

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- Definition Discloses the amount of any allowance for earnings on shareholders' investment capitalized for rate making purposes but not for the financial statements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44278-110382 + Details
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