Mergers, Acquisitions and Dispositions - Narrative (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	0 Months Ended		3 Months Ended										12 Months Ended						0 Months Ended		2 Months Ended
	Jun. 11, 2014	Mar. 20, 2013	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		Dec. 31, 2014	Nov. 01, 2014	Dec. 31, 2014	May 31, 2014	Jun. 30, 2012	Jul. 26, 2013 MW	Dec. 27, 2013 MW	Dec. 12, 2014 MW	May 30, 2012	Jan. 14, 2015	Jul. 18, 2014	Nov. 30, 2012	Feb. 28, 2012
Business Acquisition [Line Items]
Other noncurrent assets			$ 1,160,000,000					$ 964,000,000					$ 1,160,000,000		$ 964,000,000				$ 1,160,000,000		$ 1,160,000,000
Business Combination, Integration Related Costs													19,000,000		28,000,000
Equity security units	57.5
Bridge loan	3,200,000,000																					7,200,000,000
Revenues			7,255,000,000		6,912,000,000	6,024,000,000	7,237,000,000	6,163,000,000	6,502,000,000	6,141,000,000	6,082,000,000		27,429,000,000	[1]	24,888,000,000	[1]	23,489,000,000	[1]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent													1,176,000,000		2,456,000,000		854,000,000
Net income			18,000,000	[2]	993,000,000	522,000,000	90,000,000	495,000,000	738,000,000	490,000,000	(4,000,000)	[3]	1,820,000,000		1,729,000,000		1,171,000,000
Merger and integration related costs													44,000,000				141,000,000	[4]
Generating assets net book value			1,800,000,000										1,800,000,000						1,800,000,000		1,800,000,000
Expected pre-tax proceeds													1,800,000,000
Expected after-tax proceeds													1,400,000,000
Construction costs																							66,000,000
Construction time frame		20 years
Loss contingency accrual			44,000,000										44,000,000						44,000,000		44,000,000
Maximum loss contingency			105,000,000										105,000,000						105,000,000		105,000,000
Estimated future period for payment													20 years
Change in capital expenditures not paid													220,000,000		(38,000,000)		160,000,000
Operating And Maintenance Expense [Member]
Business Acquisition [Line Items]
Change in capital expenditures not paid													185,000,000		24,000,000
Development costs expensed													3,000,000		6,000,000
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Other noncurrent assets			731,000,000					645,000,000					731,000,000		645,000,000				731,000,000		731,000,000
Business Combination, Integration Related Costs			19,000,000
Revenues			4,802,000,000		4,412,000,000	3,789,000,000	4,390,000,000	3,772,000,000	4,255,000,000	4,070,000,000	3,533,000,000		17,393,000,000		15,630,000,000		14,437,000,000
Comprehensive Income (Loss), Net of Tax, Attributable to Parent													769,000,000		761,000,000		156,000,000
Net income			(91,000,000)		771,000,000	340,000,000	(185,000,000)	269,000,000	490,000,000	330,000,000	(18,000,000)		1,019,000,000		1,060,000,000		558,000,000
Merger and integration related costs													44,000,000				32,000,000	[4]
Expected period of completion													10 years
Loss contingency accrual			44,000,000										44,000,000						44,000,000		44,000,000
Capacity of energy construction project			150										150						150		150
Change in capital expenditures not paid													(61,000,000)	[5]	(107,000,000)	[6]	103,000,000	[7]
Development costs expensed													13,000,000		10,000,000		4,000,000
Exelon Generation Co L L C [Member] | Perryman Construction [Member]
Business Acquisition [Line Items]
Capacity of energy construction project																								120
Exelon Generation Co L L C [Member] | Fourmile Wind Project [Member]
Business Acquisition [Line Items]
Capacity of energy construction project			40										40						40		40				40
Exelon Generation Co L L C [Member] | Fair Wind Project [Member]
Business Acquisition [Line Items]
Capacity of energy construction project			30										30						30		30					30
Baltimore Gas and Electric Company [Member]
Business Acquisition [Line Items]
Other noncurrent assets			25,000,000					26,000,000					25,000,000		26,000,000				25,000,000		25,000,000
Revenues			761,000,000		697,000,000	653,000,000	1,054,000,000	794,000,000	737,000,000	653,000,000	880,000,000		3,165,000,000		3,065,000,000		2,735,000,000
Comprehensive Income (Loss), Net of Tax, Attributable to Parent													211,000,000		210,000,000		4,000,000
Net income			52,000,000		46,000,000	16,000,000	85,000,000	47,000,000	50,000,000	22,000,000	77,000,000		211,000,000		210,000,000		4,000,000
Merger and integration related costs													0				27,000,000	[4]
Maximum loss contingency																											1,700,000
Change in capital expenditures not paid													25,000,000		(48,000,000)		(4,000,000)
Regulatory assets transfer changes											8,000,000						272,000,000
Commonwealth Edison Co [Member]
Business Acquisition [Line Items]
Other noncurrent assets			271,000,000					291,000,000					271,000,000		291,000,000				271,000,000		271,000,000
Revenues			1,079,000,000		1,222,000,000	1,128,000,000	1,134,000,000	1,068,000,000	1,156,000,000	1,080,000,000	1,160,000,000		4,564,000,000		4,464,000,000		5,443,000,000
Comprehensive Income (Loss), Net of Tax, Attributable to Parent													408,000,000		249,000,000		380,000,000
Net income			73,000,000		126,000,000	111,000,000	98,000,000	109,000,000	126,000,000	96,000,000	(81,000,000)		408,000,000		249,000,000		379,000,000
Merger and integration related costs													0				0	[4]
Change in capital expenditures not paid													78,000,000		(8,000,000)		15,000,000
PECO Energy Co [Member]
Business Acquisition [Line Items]
Other noncurrent assets			34,000,000					38,000,000					34,000,000		38,000,000				34,000,000		34,000,000
Revenues			750,000,000		693,000,000	656,000,000	993,000,000	805,000,000	728,000,000	672,000,000	895,000,000		3,094,000,000		3,100,000,000		3,186,000,000
Comprehensive Income (Loss), Net of Tax, Attributable to Parent													352,000,000		395,000,000		382,000,000
Net income			98,000,000		81,000,000	84,000,000	89,000,000	102,000,000	92,000,000	72,000,000	121,000,000		352,000,000		395,000,000		381,000,000
Merger and integration related costs													0				0	[4]
Change in capital expenditures not paid													0		13,000,000		26,000,000
Minimum [Member]
Business Acquisition [Line Items]
Construction costs			95,000,000										95,000,000						95,000,000		95,000,000
Development of new generation cost			600,000,000										600,000,000						600,000,000		600,000,000
Expected new generation (in MW)													285
Maximum [Member]
Business Acquisition [Line Items]
Construction costs			120,000,000										120,000,000						120,000,000		120,000,000
Development of new generation cost			650,000,000										650,000,000						650,000,000		650,000,000
Expected new generation (in MW)													300
Subsequent Event [Member]
Business Acquisition [Line Items]
Aggregate value of customer rate credit programs																												62,000,000
Aggregate value of energy efficiency programs																												15,000,000
Pepco Holdings [Member]
Business Acquisition [Line Items]
Share price	$ 35																												$ 27.25
Other noncurrent assets			126,000,000										126,000,000						126,000,000		126,000,000
Other long-term investments																													18,000,000
Other long-term investments, maximum																													180,000,000
Total acquisition costs																													7,200,000,000
Proposed customer benefit package																													100,000,000
Business Acquisition, Transaction Costs			179,000,000										179,000,000						179,000,000		179,000,000
Business Combination, Integration Related Costs													48,000,000
Business Combination, Acquisition Related Costs													131,000,000
Expected debt issuance													3,500,000,000
Cash funding from non-core asset sale			1,000,000,000										1,000,000,000						1,000,000,000		1,000,000,000
Equity security units	23.0
Subordinated junior notes	1,200,000,000
Pepco Holdings [Member] | Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Capacity of energy construction project			125										125						125		125
Pepco Holdings [Member] | Bridge Loan [Member]
Business Acquisition [Line Items]
Line of credit facility, maximum borrowing capacity	7,200,000,000
Pepco Holdings [Member] | Minimum [Member]
Business Acquisition [Line Items]
Business exit costs													259,000,000
Pepco Holdings [Member] | Maximum [Member]
Business Acquisition [Line Items]
Business exit costs													293,000,000
Intergrys Energy Group Inc [Member] | Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Total consideration transferred																				332,000,000
Payments to acquire businesses													319,000,000
Liabilities incurred in acquisition																			13,000,000
Bargain purchase gain (after-tax)																				28,000,000
Revenues																					386,000,000
Net income																					(42,000,000)
Derivative, Loss on Derivative																				108,000,000
Merger and integration related costs																					7,000,000
Constellation Energy Group Acquisition [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs													22,000,000		142,000,000		804,000,000
Estimated direct investment in the State of Maryland																															1,000,000,000
Proceeds assets held for sale																														371,000,000
Regulatory assets transfer changes															17,000,000		58,000,000
Constellation Energy Group Acquisition [Member] | Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs															106,000,000		340,000,000
Constellation Energy Group Acquisition [Member] | Baltimore Gas and Electric Company [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs															6,000,000		182,000,000
Revenues															3,065,000,000		2,091,000,000
Net income															210,000,000		(31,000,000)
Regulatory assets transfer changes															6,000,000		22,000,000
Constellation Energy Group Acquisition [Member] | Commonwealth Edison Co [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs															16,000,000		41,000,000
Regulatory assets transfer changes															11,000,000		36,000,000
Constellation Energy Group Acquisition [Member] | PECO Energy Co [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs															$ 9,000,000		$ 17,000,000

[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] Relates to the integration costs to achieve distribution synergies related to the Constellation merger transaction. See Note 4 — Mergers, Acquisitions, and Dispositions for more information on Constellation merger-related commitments.

[5] Includes $170 million of changes in capital expenditures not paid between December 31, 2014 and 2013 related to Antelope Valley.

[6] Includes $55 million of changes in capital expenditures not paid between December 31, 2013 and 2012 related to Antelope Valley.

[7] Includes $127 million of changes in capital expenditures not paid between December 31, 2012 and 2011 related to Antelope Valley.