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Mergers, Acquisitions and Dispositions Purchase Price Allocation Table - FitzPatrick (Details) - USD ($) $ in Millions |  | 12 Months Ended
--- | --- | ---
Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Business Acquisition [Line Items] |  |  |  |
Payments to Acquire Businesses, Gross |  | $ 154 | $ 208 | $ 6,923
Business Combination, Bargain Purchase, Gain Recognized, Amount |  | 0 | 233 | 0
Exelon Generation Co L L C [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Payments to Acquire Businesses, Gross |  | 154 | 208 | 293
Business Combination, Bargain Purchase, Gain Recognized, Amount |  | $ 0 | 233 | $ 0
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Payments to Acquire Businesses, Gross |  |  | 110 |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets |  |  | 110 |
Business Combination, Consideration Transferred, Other | $ 179 |  | 54 |
Business Combination, Consideration Transferred | 289 |  | 289 |
Current assets |  |  | 60 |
Property, plant and equipment |  |  | 298 |
Unamortized energy contracts |  |  | 807 |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets |  |  | 114 |
Total assets |  |  | 1,279 |
Current liabilities |  |  | 6 |
Unamortized energy contract liabilities |  |  | (444) |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent |  |  | 149 |
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRegulatedLiabilities |  |  | 110 |
Other liabilities |  |  | (15) |
Total liabilities |  |  | 757 |
Total net assets |  |  | 522 |
_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRetirmentObligations |  |  | 33 |
Business Combination, Bargain Purchase, Gain Recognized, Amount |  |  | 233 |
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Cash and Cash Equivalents [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Payments to Acquire Businesses, Gross |  |  | $ 125 |
Business Combination, Consideration Transferred | $ 110 |  |  |

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