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Stock-Based Compensation Plans - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 23, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Allocated Share-based Compensation Expense |  | $ 208 | $ 191 | $ 175 | [1]
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense |  |  |  | (18) |
Allocated Share-based Compensation Expense, Net of Tax |  | 154 | 117 | 107 | [1]
Performance Shares [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Allocated Share-based Compensation Expense |  | 143 | 107 | 93 | [1]
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense |  | (16) | (29) | (18) |
Restricted Stock Units (RSUs) [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Allocated Share-based Compensation Expense |  | 57 | 77 | 75 | [1]
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense |  | (28) | (35) | (27) |
Employee Stock Option [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Allocated Share-based Compensation Expense |  | 0 | 0 | 0 | [1]
Stock Compensation Plan [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Allocated Share-based Compensation Expense |  | 8 | 7 | 7 | [1]
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense |  | $ (54) | $ (74) | $ (68) | [1]
Predecessor [Member] | Pepco Holdings LLC [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Allocated Share-based Compensation Expense | $ 3 |  |  |  |
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense | (1) |  |  |  |
Allocated Share-based Compensation Expense, Net of Tax | 2 |  |  |  |
Predecessor [Member] | Pepco Holdings LLC [Member] | Performance Shares [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Allocated Share-based Compensation Expense | 1 |  |  |  |
Predecessor [Member] | Pepco Holdings LLC [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Allocated Share-based Compensation Expense | 2 |  |  |  |
Predecessor [Member] | Pepco Holdings LLC [Member] | Employee Stock Option [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Allocated Share-based Compensation Expense | $ 0 |  |  |  |
[1] | (a)2016 amounts include expense related to stock-based compensation granted to eligible PHI employees since the merger date of March 23, 2016.

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The amount of expense, net of income tax, recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References No definition available. + Details
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- Definition The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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