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Earnings Per Share Earnings Per Share - Narrative (Details) - shares shares in Millions |  | 12 Months Ended
--- | --- | ---
Jun. 01, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Equity units issued [Member] |  |  |  |
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] |  |  |  |
Stock Issued During Period, Shares, Treasury Stock Reissued | 33 |  |  |
Pepco Holdings [Member] |  |  |  |
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] |  |  |  |
Stock options not included in the calculation of diluted common shares outstanding (less than 1 million related to PHI merger) |  | 0 | 0 | 0
Employee Stock Option [Member] |  |  |  |
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] |  |  |  |
Stock options not included in the calculation of diluted common shares outstanding (less than 1 million related to PHI merger) |  | 3 | 8 | 12

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- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Number of treasury shares (units) reissued during the period, excluding reissuance of shares (units) held in treasury used to satisfy equity-based compensation obligations exercised by the holders of such rights. Upon reissuance of shares (units) from treasury, either the common or preferred stock (unit) reissued is outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644 + Details
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