Income Taxes - Components of Income Tax Expense (Benefit) from Continuing Operations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Taxes [Line Items]
Income taxes	$ 666us-gaap_IncomeTaxExpenseBenefit	$ 1,044us-gaap_IncomeTaxExpenseBenefit	$ 627us-gaap_IncomeTaxExpenseBenefit
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Income taxes	207	615	500
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Income taxes	268	152	239
PECO Energy Co [Member]
Income Taxes [Line Items]
Income taxes	114	162	127
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current	0	0	0
Income taxes	140	134	7
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Current	121	744	37
Deferred	576	140	701
Investment Tax Credit	20	15	11
Internal Revenue Service (IRS) [Member] \| Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Current	360	250	104
Deferred	(35)	360	326
Investment Tax Credit	16	11	6
Internal Revenue Service (IRS) [Member] \| Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current	(171)	160	(40)
Deferred	395	(27)	237
Investment Tax Credit	2	2	2
Internal Revenue Service (IRS) [Member] \| PECO Energy Co [Member]
Income Taxes [Line Items]
Current	28	126	88
Deferred	87	23	25
Investment Tax Credit	0	1	2
Internal Revenue Service (IRS) [Member] \| Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current	24	9	(97)
Deferred	90	100	101
Investment Tax Credit	1	1	1
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Current	42	181	(25)
Deferred	(53)	(6)	(75)
State and Local Jurisdiction [Member] \| Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Current	35	50	(12)
Deferred	(137)	(34)	88
State and Local Jurisdiction [Member] \| Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current	7	50	6
Deferred	39	(29)	38
State and Local Jurisdiction [Member] \| PECO Energy Co [Member]
Income Taxes [Line Items]
Current	(2)	16	4
Deferred	1	(2)	12
State and Local Jurisdiction [Member] \| Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Deferred	$ 27	$ 26	$ 4

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Amount of current income tax expense (benefit) pertaining to taxable income (loss) from continuing operations.

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Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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The amount deducted from an entities' taxes, reflecting a percentage of an amount invested in certain assets spread over the useful life of those assets; includes deferred investment tax credits.

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