Mergers, Acquisitions and Dispositions - Summary of Integrys Energy Group Acquisition (Details) (Exelon Generation Co L L C [Member], Intergrys Energy Group Inc [Member], USD $) In Millions, unless otherwise specified	0 Months Ended
Nov. 01, 2014	Nov. 01, 2014
Exelon Generation Co L L C [Member] \| Intergrys Energy Group Inc [Member]
Business Acquisition [Line Items]
Total consideration transferred	$ 332
Working capital assets	389	389
Mark-to-market derivative assets	185	185
Unamortized energy contracts	115	115
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	48	48
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities	(195)	(195)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Derivative Liabilities	(57)	(57)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities	(109)	(109)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent	(16)	(16)
Total net assets	360	360
Bargain purchase gain (after-tax)	$ 28

Mergers, Acquisitions and Dispositions - Summary of Integrys Energy Group Acquisition (Details) (Exelon Generation Co L L C [Member], Intergrys Energy Group Inc [Member], USD $)
In Millions, unless otherwise specified

0 Months Ended

Nov. 01, 2014

Exelon Generation Co L L C [Member] | Intergrys Energy Group Inc [Member]

Business Acquisition [Line Items]

Total consideration transferred

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Working capital assets

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Mark-to-market derivative assets

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Unamortized energy contracts

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Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities

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Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Derivative Liabilities

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Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities

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Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent

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Total net assets

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Bargain purchase gain (after-tax)

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