Supplemental Financial Information - Supplemental Cash Flow Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)	$ 940		$ 866		$ 761
Income taxes (net of refunds)	314		112		(171)
Pension and non-pension postretirement benefit costs	560		825		820
Income (Loss) from Equity Method Investments	20		(10)		91
Provision for uncollectible accounts	156		101		164
Provision for excess and obsolete inventory	5		9		6
Stock-based compensation costs	91		120		94
Other decommissioning related-activity	(132)	[1]	(169)	[1]	(145)	[1]
Energy-related options	122	[2]	104	[2]	160	[2]
Amortization of regulatory asset related to debt costs	11		12		18
Amortization of rate stabilization deferral	65		66		57
Amortization of debt fair value adjustment	(23)		(34)		(34)
Merger-related commitments	44				141	[3]
Discrete impacts from EIMA	53	[4]	(271)	[4]	(96)	[5]
Amortization of debt costs	53		18		19
Lower of cost or market inventory adjustment	29
Other	(2)		(53)		(30)
Total other non-cash operating activities	1,054		718		1,364
Under/over-recovered energy and transmission costs	47		12		71
Other regulatory assets and liabilities	(167)		(64)		(404)
Increase (Decrease) in Deposits	(241)	[6]
Other current assets	7		(165)		213
Other noncurrent assets and liabilities	(204)		322		(248)
Total changes in other assets and liabilities	(558)		102		(368)
Change in ARC	72		(128)		781
Change in capital expenditures not paid	220		(38)		160
Consolidated VIE dividend to noncontrolling	421		63
Fair value of net assets recorded upon CENG consolidation (f)	(3,400)	[7]
Issuance of equity units	131	[8]
Other Cost and Expense, Operating	8,568		7,270		7,961
Antelope Valle [Member]
Supplemental Cash Flow Information [Line Items]
Change in capital expenditures not paid	170		55		127
Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options	70	[9]
Indemnification of like-kind exchange position	0	[10]	0	[11]
Exelon Generation Co L L C [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)	322		291		286
Income taxes (net of refunds)	227		(18)		175
Pension and non-pension postretirement benefit costs	249		345		341
Income (Loss) from Equity Method Investments	20		(10)		91
Provision for uncollectible accounts	14		10		22
Provision for excess and obsolete inventory	5		9		6
Stock-based compensation costs	0		0		0
Other decommissioning related-activity	(132)	[1]	(169)	[1]	(145)	[1]
Energy-related options	122	[2]	104	[2]	160	[2]
Amortization of regulatory asset related to debt costs	0		0		0
Amortization of rate stabilization deferral	0		0		0
Amortization of debt fair value adjustment	(23)		(34)		(34)
Merger-related commitments	44				32	[3]
Discrete impacts from EIMA	0	[4]	0	[4]	0	[5]
Amortization of debt costs	12		10		11
Lower of cost or market inventory adjustment	29
Other	6		5		0
Total other non-cash operating activities	346		270		518
Under/over-recovered energy and transmission costs	0		0		0
Other regulatory assets and liabilities	0		0		0
Increase (Decrease) in Deposits	(241)	[6]
Other current assets	81		(151)		(30)
Other noncurrent assets and liabilities	(89)		15		(98)
Total changes in other assets and liabilities	(249)		(136)		(128)
Change in ARC	72		(128)		781
Change in capital expenditures not paid	(61)	[12]	(107)	[13]	103	[14]
Consolidated VIE dividend to noncontrolling	(1,548)		63
Fair value of net assets recorded upon CENG consolidation (f)	(3,400)	[7]
Issuance of equity units	0	[8]
Other Cost and Expense, Operating	4,943		3,960		4,398
Exelon Generation Co L L C [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options	70	[9]
Indemnification of like-kind exchange position	0	[10]	0	[11]
Commonwealth Edison Co [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)	292		283		288
Income taxes (net of refunds)	(6)		33		(42)
Pension and non-pension postretirement benefit costs	162		308		282
Income (Loss) from Equity Method Investments	0		0
Provision for uncollectible accounts	26		(15)		42
Provision for excess and obsolete inventory	0		0		1
Stock-based compensation costs	0		0		0
Other decommissioning related-activity	0	[1]	0	[1]	0	[1]
Energy-related options	0	[2]	0	[2]	0	[2]
Amortization of regulatory asset related to debt costs	8		9		13
Amortization of rate stabilization deferral	0		0		0
Amortization of debt fair value adjustment	0		0		0
Merger-related commitments	0				0	[3]
Discrete impacts from EIMA	53	[4]	(271)	[4]	(96)	[5]
Amortization of debt costs	4		1		5
Lower of cost or market inventory adjustment	0
Other	2		(4)		5
Total other non-cash operating activities	255		28		252
Under/over-recovered energy and transmission costs	36		(35)		28
Other regulatory assets and liabilities	(13)		(43)		(68)
Increase (Decrease) in Deposits	0	[6]
Other current assets	(10)		51		33
Other noncurrent assets and liabilities	32		268	[15]	(95)
Total changes in other assets and liabilities	45		241		(102)
Change in ARC	0		0		2
Change in capital expenditures not paid	78		(8)		15
Fair value of net assets recorded upon CENG consolidation (f)	0	[7]
Issuance of equity units	0	[8]
Indemnification of like-kind exchange position	273		0		0
Other Cost and Expense, Operating	1,263		1,211		1,182
Commonwealth Edison Co [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options	0	[9]
Indemnification of like-kind exchange position	5	[10]	176	[11]
PECO Energy Co [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)	94		95		113
Income taxes (net of refunds)	85		70		(64)
Pension and non-pension postretirement benefit costs	36		43		50
Income (Loss) from Equity Method Investments	0		0		0
Provision for uncollectible accounts	52		61		60
Provision for excess and obsolete inventory	0		0		0
Stock-based compensation costs	0		0		0
Other decommissioning related-activity	0	[1]	0	[1]	0	[1]
Energy-related options	0	[2]	0	[2]	0	[2]
Amortization of regulatory asset related to debt costs	3		3		3
Amortization of rate stabilization deferral	0		0		0
Amortization of debt fair value adjustment	0		0		0
Merger-related commitments	0				0	[3]
Discrete impacts from EIMA	0	[4]	0	[4]	0	[5]
Amortization of debt costs	2		2		3
Lower of cost or market inventory adjustment	0
Other	(1)		(1)		9
Total other non-cash operating activities	92		108		125
Under/over-recovered energy and transmission costs	0		9		20
Other regulatory assets and liabilities	(16)		(16)		18
Increase (Decrease) in Deposits	0	[6]
Other current assets	(2)		13		(12)
Other noncurrent assets and liabilities	1		(12)		(10)
Total changes in other assets and liabilities	(17)		(6)		16
Change in ARC	0		0		0
Change in capital expenditures not paid	0		13		26
Fair value of net assets recorded upon CENG consolidation (f)	0	[7]
Issuance of equity units	0	[8]
Indemnification of like-kind exchange position	24		27		9
Other Cost and Expense, Operating	767		647		698
PECO Energy Co [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options	0	[9]
Indemnification of like-kind exchange position	0	[10]	0	[11]
Baltimore Gas and Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)	111		130		136
Income taxes (net of refunds)	(21)		42		(112)
Pension and non-pension postretirement benefit costs	64		56		57
Income (Loss) from Equity Method Investments	0		0		0
Provision for uncollectible accounts	64		44		44
Provision for excess and obsolete inventory	0		0		0
Stock-based compensation costs	0		0		0
Other decommissioning related-activity	0	[1]	0	[1]	0	[1]
Energy-related options	0	[2]	0	[2]	0	[2]
Amortization of regulatory asset related to debt costs	0		0		2
Amortization of rate stabilization deferral	65		66		67
Amortization of debt fair value adjustment	0		0		0
Merger-related commitments	0				27	[3]
Discrete impacts from EIMA	0	[4]	0	[4]	0	[5]
Amortization of debt costs	2		2		2
Lower of cost or market inventory adjustment	0
Other	(15)		(15)		(6)
Total other non-cash operating activities	180		153		193
Under/over-recovered energy and transmission costs	11		38		26
Other regulatory assets and liabilities	(121)		(71)		(112)
Increase (Decrease) in Deposits	0	[6]
Other current assets	(44)		(8)		(7)
Other noncurrent assets and liabilities	(9)		(23)		8
Total changes in other assets and liabilities	(163)		(64)		(85)
Change in ARC	0		4		0
Change in capital expenditures not paid	25		(48)		(4)
Fair value of net assets recorded upon CENG consolidation (f)	0	[7]
Issuance of equity units	0	[8]
Indemnification of like-kind exchange position	0		0		66
Other Cost and Expense, Operating	614		551		622
Baltimore Gas and Electric Company [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options	0	[9]
Indemnification of like-kind exchange position	0	[10]	0	[11]
Exelon Consolidations [Member]
Supplemental Cash Flow Information [Line Items]
Income (Loss) from Equity Method Investments	22
Total changes in other assets and liabilities			105
Severance [Member]
Supplemental Cash Flow Information [Line Items]
Other Cost and Expense, Operating					99
Severance [Member] | Exelon Generation Co L L C [Member]
Supplemental Cash Flow Information [Line Items]
Other Cost and Expense, Operating					34
Severance [Member] | Commonwealth Edison Co [Member]
Supplemental Cash Flow Information [Line Items]
Other Cost and Expense, Operating					0
Severance [Member] | PECO Energy Co [Member]
Supplemental Cash Flow Information [Line Items]
Other Cost and Expense, Operating					0
Severance [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Other Cost and Expense, Operating					0
Constellation Energy Group Acquisition [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling			63		7,365
Constellation Energy Group Acquisition [Member] | Exelon Generation Co L L C [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling			63		5,264
Constellation Energy Group Acquisition [Member] | Commonwealth Edison Co [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling			0		0
Constellation Energy Group Acquisition [Member] | PECO Energy Co [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling			0		0
Constellation Energy Group Acquisition [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Consolidated VIE dividend to noncontrolling			$ 0		$ 0

[1] Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning.

[2] Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations.

[3] 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.

[4] Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through a pre-established performance-based formula rate tariff. See Note 3 — Regulatory Matters for more information.

[5] Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through pre-established performance-based formula rate tariff. See Note 3 — Regulatory Matters.

[6] Relates primarily to cash deposits made to ISO's/RTO's.

[7] See Note 5 — Investment in Constellation Energy Nuclear Group, LLC for additional information.

[8] Relates to the present value of the contract payments for the equity units issued by Exelon. See Note 19 — Common Stock for additional information.

[9] Relates to the nuclear fuel procurement contracts for the purchase of fixed quantities of uranium, which was delivered to Generation on June 30, 2014 and September 24, 2014. Generation is required to make payments starting June 30, 2016, with the final payment being due no later than June 30, 2018.

[10] See Note 14 — Income Taxes for discussion of the like-kind exchange tax position.

[11] See Note 14 — Income Taxes for discussion of the like-kind exchanged tax position.

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

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

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

[15] Relates primarily to interest payable related to like-kind exchange tax position. See Note 14 — Income Taxes for discussion of the like-kind exchange tax position.