Changes in Accumulated Other Comprehensive Income - Reclassifications out of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013		Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	$ 7,255		$ 6,912	$ 6,024	$ 7,237	$ 6,163	$ 6,502	$ 6,141	$ 6,082		$ 27,429	[1]	$ 24,888	[1]	$ 23,489	[1]
Interest expense											(610)		(896)		(575)
Prior service costs											19		0		(1)
Sale of equity method investment											455		460		353
Total income (loss) in equity method investments											(20)		10		(91)
Income before income taxes											2,486		2,773		1,798
Income tax benefit (expense)											(666)		(1,044)		(627)
Net income	18	[2]	993	522	90	495	738	490	(4)	[3]	1,820		1,729		1,171
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income											116	[4]	64	[4]
Reclassification out of Accumulated Other Comprehensive Income [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income											(2)	[4]
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues											(2)	[4]
Income before income taxes											195	[4]	461	[4]
Income tax benefit (expense)											(78)	[4]	(184)	[4]
Net income											117	[4]	277	[4]
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues											195	[4]	464	[4]
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense													(3)	[4]
Reclassification out of Accumulated Other Comprehensive Income [Member] | Equity Method Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Sale of equity method investment											5	[4]
Equity in losses of unconsolidated affiliates											193	[4]
Total income (loss) in equity method investments													(8)	[4]
Income before income taxes													(8)	[4]
Income tax benefit (expense)													3	[4]
Net income													(5)	[4]
Exelon Generation Co L L C [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	4,802		4,412	3,789	4,390	3,772	4,255	4,070	3,533		17,393		15,630		14,437
Interest expense											50		(2)		(55)
Sale of equity method investment											406		355		246
Total income (loss) in equity method investments											(20)		10		(91)
Income tax benefit (expense)											(207)		(615)		(500)
Net income	(91)		771	340	(185)	269	490	330	(18)		1,019		1,060		558
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income											236	[4]	408	[4]
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income before income taxes											195	[4]	683	[4]
Income tax benefit (expense)											(78)	[4]	(270)	[4]
Net income											117	[4]	413	[4]
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues											195	[4]	683	[4]
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense													0	[4]
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Equity Method Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Sale of equity method investment											5	[4]
Equity in losses of unconsolidated affiliates											193	[4]
Total income (loss) in equity method investments													(8)	[4]
Income before income taxes													(8)	[4]
Income tax benefit (expense)													3	[4]
Net income													(5)	[4]
Other Equity Investment Reclassified Out of Accumulated Other Comprehensive Income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension Nuclear Decommissioning Attributable To Equity Method Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income before income taxes											198	[4]
Income tax benefit (expense)											(79)	[4]
Net income											119	[4]
Other Equity Investment Reclassified Out of Accumulated Other Comprehensive Income [Member] | Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension Nuclear Decommissioning Attributable To Equity Method Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income before income taxes											198	[4]
Income tax benefit (expense)											(79)	[4]
Net income											119	[4]
Pension Plan, Defined Benefit [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Prior service costs											46	[4],[5]	(2)	[4],[5]
Actuarial gains/losses											(239)	[4],[5]	(339)	[4],[5]
Income before income taxes											(193)	[4]	(342)	[4]
Income tax benefit (expense)											75	[4]	134	[4]
Net income											(118)	[4]	(208)	[4]
Pension Plan, Defined Benefit [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Equity Method Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Actuarial gains/losses													$ (1)	[4],[6]

[1] For the years ended December 31, 2014, 2013 and 2012, utility taxes of $89 million, $79 million and $82 million, respectively, are included in revenues and expenses for Generation. For the years ended December 31, 2014, 2013 and 2012, utility taxes of $238 million, $241 million and $239 million, respectively, are included in revenues and expenses for ComEd. For the years ended December 31, 2014, 2013 and 2012, utility taxes of $128 million, $129 million and $141 million, respectively, are included in revenues and expenses for PECO. For the years ended December 31, 2014, December 31, 2013 and for the period of March 12, 2012 through December 31, 2012, utility taxes of $86 million, $82 million and $59 million are included in revenues and expenses for BGE, respectively.

[2] Includes charges to earnings related to the impairments of certain generating assets which were held for sale and certain Upstream exploration assets. See Note 8—Impairment of Long-Lived Assets of the Combined Notes to Consolidated Financial Statements for additional information.

[3] Includes $265 million of interest expense related to the remeasurement of Exelon’s like-kind exchange tax position in the first quarter of 2013. See Note 14—Income Taxes of the Combined Notes to Consolidated Financial Statements for additional information.

[4] Amounts in parenthesis represent a decrease in net income.

[5] This accumulated other comprehensive income component is included in the computation of net periodic pension and OPEB cost (see Note 16 — Retirement Benefits for additional details).

[6] Amortization of the deferred compensation unit plan is allocated to capital and operating and maintenance expense.