Supplemental Financial Information - Cash Flow (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended						37 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2012
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	$ 1,893		$ 1,712		$ 1,284
Regulatory assets	212		129		63
Amortization of intangible assets, net	48		40
Amortization of energy contract assets and liabilities	430		1,110
Nuclear fuel	921	[1]	848	[1]	755	[1]
Asset retirement obligation accretion	275	[2]	240	[2]	214	[2]
Total depreciation, amortization and accretion	3,779		4,079		2,316
Cash Paid Refunded During Year [Abstract]
Interest (net of amount capitalized)	866		761		649
Income taxes (net of refunds)	112		(171)		(457)
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	825		820		542
Provision for uncollectible accounts	101		164		121
Provision for Obsolete Inventory	9
Stock-based compensation costs	120		94		67
Other Decommissioning Related Activity	169		145		(16)
Energy-related options	104	[3]	160	[3]	137	[3]
ARO adjustment			0		0
Amortization of regulatory asset related to debt costs	12		18		21
Amortization of rate stabilization deferral	66		57
Amortization of debt fair value adjustment	34		(34)
Accrual for Illinois utility distribution tax refund					0
Uncollectible accounts recovery					14
APR SO2 allowances impairment			0		0
Discrete impacts from 2010 Rate Case Order					32	[4]
Bargain purchase gain					(36)
Discrete impacts from EIMA	(271)	[5]	96	[5]	82
Merger related commitments	0	[6]	141	[6]
Severance Costs	0		99
Gain (loss) on equity method investments	(10)		91		1
Impairment in investment of direct financing leases	14	[7]
Impairment Of Long Lived Asets Held For Use	149	[8]
Amortization of debt costs	(18)		19
Other	(58)		(11)		2
Total other noncash operating activities	(876)		(1,383)		(770)
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	12		71		(45)
Other regulatory assets and liabilities	(64)		(404)
Other current assets and liabilities	(165)		213		(101)
Other noncurrent assets and liabilities	319		(248)		122
Total changes in other assets and liabilities	102		(368)		(24)
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Change in ARC	(128)		781		186
Capital expenditures not paid	(38)		160		96
Purchase accounting adjustments			0
Merger with Constellation, common stock issued			7,365
Consolidated VIE dividend to non-controlling interest	63
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures	74		103
Smart Grid Grant Reimbursements	95		113
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	813		733		570
Regulatory assets	0		0		0
Amortization of intangible assets, net	43		35
Amortization of energy contract assets and liabilities	507		1,110
Nuclear fuel	921	[1]	848	[1]	755	[1]
Asset retirement obligation accretion	275	[2]	240	[2]	214	[2]
Total depreciation, amortization and accretion	2,559		2,966		1,539
Cash Paid Refunded During Year [Abstract]
Interest (net of amount capitalized)	291		286		158
Income taxes (net of refunds)	(18)		175		347
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	345		341		249
Provision for uncollectible accounts	10		22		0
Provision for Obsolete Inventory	9		6				18
Other Decommissioning Related Activity	169		145		(16)
Energy-related options	104	[3]	160	[3]	137	[3]
ARO adjustment			0		0
Amortization of debt fair value adjustment	34		(34)
APR SO2 allowances impairment			0		0
Bargain purchase gain					(36)
Merger related commitments	0		32	[6]
Severance Costs	0		34
Gain (loss) on equity method investments	(10)		91		1
Impairment Of Long Lived Asets Held For Use	149	[8]
Amortization of debt costs	(10)		11
Other	0		19		55
Total other noncash operating activities	(414)		(537)		(421)
Changes In Other Assets and Liabilities [Abstract]
Other current assets and liabilities	(151)		(30)		(23)
Other noncurrent assets and liabilities	15		(98)		(34)
Total changes in other assets and liabilities	(136)		(128)		(57)
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Change in ARC	(128)		781		186
Capital expenditures not paid	(107)	[9]	103	[10]	125
Purchase accounting adjustments			0
Merger with Constellation, common stock issued			5,264
Consolidated VIE dividend to non-controlling interest	(63)
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	545		525		502
Regulatory assets	119		80		52
Amortization of intangible assets, net	5		5
Nuclear fuel	0		0		0
Asset retirement obligation accretion	0		0	[2]	0	[2]
Total depreciation, amortization and accretion	669		610		554
Cash Paid Refunded During Year [Abstract]
Interest (net of amount capitalized)	283		288		296
Income taxes (net of refunds)	33		(42)		(676)
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	308		282		213
Provision for uncollectible accounts	(15)		42		57
Provision for Obsolete Inventory	0		1
ARO adjustment			0		0
Amortization of regulatory asset related to debt costs	9		13		18
Accrual for Illinois utility distribution tax refund					0
Uncollectible accounts recovery					14
Discrete impacts from 2010 Rate Case Order					32	[4]
Discrete impacts from EIMA	(271)	[5]	96	[5]	82
Merger related commitments	0	[6]
Gain (loss) on equity method investments	0		0		0
Amortization of debt costs	(1)		5
Other	(4)		5		(4)
Total other noncash operating activities	(28)		(252)		(184)
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	(35)		28		(49)
Other regulatory assets and liabilities	(43)		(68)		44
Other current assets and liabilities	(2)		(7)		(14)
Other noncurrent assets and liabilities	268		(95)		64
Total changes in other assets and liabilities	188		(142)		45
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Change in ARC	0		2
Capital expenditures not paid	(8)		15		7
Allocation Of Tax Benefit From Parent	176		11		11
Indemnification of like-kind exchange position	(176)
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	219		207		191
Regulatory assets	9		10		11
Nuclear fuel	0		0		0
Asset retirement obligation accretion	0		0	[2]	0	[2]
Total depreciation, amortization and accretion	228		217		202
Cash Paid Refunded During Year [Abstract]
Interest (net of amount capitalized)	95		113		128
Income taxes (net of refunds)	70		(64)		(65)
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	43		50		32
Provision for uncollectible accounts	61		60		64
ARO adjustment			0		0
Amortization of regulatory asset related to debt costs	3		3		3
Amortization of debt costs	(2)		3
Other	(1)		9		1
Total other noncash operating activities	(108)		(125)		(100)
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	9		20		4
Other regulatory assets and liabilities	(16)		18		26
Other current assets and liabilities	13		(12)
Other noncurrent assets and liabilities	(12)		(10)		(4)
Total changes in other assets and liabilities	(6)		16		14
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Capital expenditures not paid	13		26		(35)
Allocation Of Tax Benefit From Parent	27		9		18
Indemnification of like-kind exchange position	(27)		(9)		(18)
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures	27		56
Smart Grid Grant Reimbursements	37		66
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	264		245		224
Regulatory assets	84		53		50
Total depreciation, amortization and accretion	348		298		274
Cash Paid Refunded During Year [Abstract]
Interest (net of amount capitalized)	130		136		122
Income taxes (net of refunds)	42		(112)		(54)
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	56		57		51
Provision for uncollectible accounts	44		44		44
Amortization of regulatory asset related to debt costs			2		2
Amortization of rate stabilization deferral	66		67		57
Deferral of storm costs	(16)				16
Merger related commitments			27	[6]
Amortization of debt costs	(2)		2
Other	(15)		(6)		(9)
Total other noncash operating activities	(153)		(193)		(129)
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	38		26		(52)
Other regulatory assets and liabilities	(71)		(112)		10
Other current assets and liabilities	(8)		(7)		(88)
Other noncurrent assets and liabilities	(23)		8		(31)
Total changes in other assets and liabilities	(64)		(85)		(161)
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Change in ARC			4
Capital expenditures not paid	(48)		(4)		(7)
Indemnification of like-kind exchange position	0		(66)		0
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures	47		47
Smart Grid Grant Reimbursements	$ 58		$ 47

[1] Included in revenues or fuel expense, or operating revenues on the Registrants' Consolidated Statements of Operations and Comprehensive Income.

[2] Included in operating and maintenance expense on the Registrants' Consolidated Statements of Operations and Comprehensive Income.

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

[4] In May 2011, as a result of the 2010 Rate Case order, ComEd recorded one-time benefits to reestablish previously expensed plant balances and to recover previously incurred costs related to Exelon's 2009 restructuring plan. 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 a pre-established performance-based formula rate tariff. See Note 3 – Regulatory Matters for more information.

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

[7] Relates to an other than temporary decline in the estimated residual value of one of Exelon’s direct financing leases. See Note 8 – Impairment of Long-Lived Assets for more information.

[8] Relates to the cancellation of uprate projects and write down of certain wind projects at Generation. See Note 8 – Impairment of Long-Lived Assets for more information.

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

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