Supplemental Financial Information - Cash Flow (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	$ 942		$ 806
Regulatory assets	112		56
Amortization of intangible assets, net	22		14
Amortization of energy contract assets and liabilities	306	[1]	485	[1]
Nuclear fuel	454	[1]	419	[1]
Asset retirement obligation accretion	136	[2]	115	[2]
Total depreciation, amortization and accretion	1,972		1,895
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	409		400
Provision for uncollectible accounts	55		60
Provision for Obsolete Inventory	13
Stock-based compensation costs	70		56
Other Decommissioning Related Activity	(62)	[3]	(62)	[3]
Energy-related options	65	[4]	64	[4]
Amortization of regulatory asset related to debt costs	6		9
Amortization of rate stabilization deferral	29		15
Amortization of debt fair value adjustment	(22)		(26)
Discrete impacts from EIMA	(126)	[5]	69	[5]
Merger related commitments	(6)	[6]	188	[7]
Severance Costs			119
Gain (loss) on equity method investments	30		79
Impairment in investment of direct financing leases	14
Impairment Of Long Lived Asets Held For Use	110
Amortization of debt costs	8
Other	(17)		(12)
Total other noncash operating activities	576		959
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	(24)		(37)
Other regulatory assets and liabilities	(3)		514
Other current assets and liabilities	(123)		190
Other noncurrent assets and liabilities	277		(12)
Total changes in other assets and liabilities	133		(373)
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Merger with Constellation, common stock issued			7,365
Consolidated VIE dividend to non-controlling interest	63
Total noncash investing and financing activities	(63)		7,365
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures	41		52
Smart Grid Grant Reimbursements	50		65
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	402		343
Regulatory assets			0
Amortization of intangible assets, net	22		14
Amortization of energy contract assets and liabilities	344	[1]	532	[1]
Nuclear fuel	454	[1]	419	[1]
Asset retirement obligation accretion	136	[2]	115	[2]
Total depreciation, amortization and accretion	1,358		1,423
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	173		175
Provision for uncollectible accounts	10		(1)
Provision for Obsolete Inventory	13
Stock-based compensation costs	0
Other Decommissioning Related Activity	(62)	[3]	(62)	[3]
Energy-related options	65	[4]	64	[4]
Amortization of debt fair value adjustment	(22)		(11)
Merger related commitments			35	[7]
Severance Costs			30
Gain (loss) on equity method investments	30		79
Impairment Of Long Lived Asets Held For Use	110
Amortization of debt costs	5
Other	(7)		9
Total other noncash operating activities	315		318
Changes In Other Assets and Liabilities [Abstract]
Other current assets and liabilities	(134)		(97)
Other noncurrent assets and liabilities	(34)		(77)
Total changes in other assets and liabilities	(168)		(174)
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Merger with Constellation, common stock issued			5,272
Consolidated VIE dividend to non-controlling interest	63
Total noncash investing and financing activities	(63)		5,272
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	275		262
Regulatory assets	62		38
Amortization of intangible assets, net			0
Total depreciation, amortization and accretion	337		300
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	154		137
Provision for uncollectible accounts	4		21
Stock-based compensation costs	0
Amortization of regulatory asset related to debt costs	5		7
Discrete impacts from EIMA	(126)	[5]	69	[5]
Amortization of debt costs	2		2
Other	0		5
Total other noncash operating activities	39		241
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	(61)		(58)
Other regulatory assets and liabilities	28		39
Other current assets and liabilities	2		(1)
Other noncurrent assets and liabilities	259	[8]	(6)
Total changes in other assets and liabilities	172		(104)
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Allocation Of Tax Benefit From Parent	174
Indemnification of like-kind exchange position	0		0
Total noncash investing and financing activities	(174)
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	109		102
Regulatory assets	4		5
Amortization of intangible assets, net			0
Total depreciation, amortization and accretion	113		107
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	21		26
Provision for uncollectible accounts	27		26
Stock-based compensation costs	0
Amortization of regulatory asset related to debt costs	1		1
Severance Costs			7
Amortization of debt costs	1
Other	0		6
Total other noncash operating activities	50		66
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	19		18
Other regulatory assets and liabilities	5		(12)
Other current assets and liabilities	(62)		(110)
Other noncurrent assets and liabilities	(1)		(7)
Total changes in other assets and liabilities	(49)		(87)
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures	12		34
Smart Grid Grant Reimbursements	16		46
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	128		123
Regulatory assets	47		27
Amortization of intangible assets, net			0
Total depreciation, amortization and accretion	175		150
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	27		32
Provision for uncollectible accounts	14		17
Stock-based compensation costs	0
Amortization of regulatory asset related to debt costs	0		1
Amortization of rate stabilization deferral	29		25
Merger related commitments	(6)	[6]	28	[7]
Severance Costs			0
Other	(3)		(3)
Total other noncash operating activities	61		100
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	18		2
Other regulatory assets and liabilities	82		28
Other current assets and liabilities	99		55
Other noncurrent assets and liabilities	28		14
Total changes in other assets and liabilities	63		43
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position	0		(66)
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures	29		18
Smart Grid Grant Reimbursements	$ 34		$ 19

[1] Included in purchased power and fuel expense 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 the elimination of NDT fund-related 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 13 of the Exelon 2012 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

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

[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 5 - Regulatory Matters for more information.

[6] Relates to integration costs to achieve distribution synergies related to the merger transaction. See Note 5 - Regulatory Matters for more information.

[7] See Note 4 - Mergers and Acquisitions for more information on merger-related commitments.

[8] Relates primarily to interest payable related to like-kind exchange tax position. See Note 12 – Income Taxes for discussion of the like-kind exchange tax position.