Supplemental Financial Information - Cash Flow (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	$ 1,420		$ 1,263
Regulatory assets	153		89
Amortization of intangible assets, net	33		24
Amortization of energy contract assets and liabilities	342	[1]	731	[1]
Nuclear fuel	689	[1]	628	[1]
Asset retirement obligation accretion	207	[2]	174	[2]
Total depreciation, amortization and accretion	2,844		2,909
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	621		606
Provision for uncollectible accounts	83		120
Provision for Obsolete Inventory	7
Stock-based compensation costs	99		75
Other Decommissioning Related Activity	(110)	[3]	(108)	[3]
Energy-related options	87	[4]	119	[4]
Amortization of regulatory asset related to debt costs	9		13
Amortization of rate stabilization deferral	49		39
Amortization of debt fair value adjustment	(28)		(49)
Discrete impacts from EIMA	(206)	[5]	43	[5]
Merger related commitments	(6)	[6]	179	[7]
Severance Costs			120
Gain (loss) on equity method investments	(7)		69
Impairment in investment of direct financing leases	14
Impairment Of Long Lived Asets Held For Use	149
Amortization of debt costs	13
Other	(36)		9
Total other noncash operating activities	738		1,235
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	(47)		20
Settlement of interest rate swaps	(26)
Other regulatory assets and liabilities	50		454
Other current assets and liabilities	(169)		52
Other noncurrent assets and liabilities	205		(40)
Total changes in other assets and liabilities	(35)		(422)
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)
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures	68		75
Smart Grid Grant Reimbursements	64		85
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	610		540
Regulatory assets			0
Amortization of intangible assets, net	33		24
Amortization of energy contract assets and liabilities	398	[1]	812	[1]
Nuclear fuel	689	[1]	628	[1]
Asset retirement obligation accretion	207	[2]	174	[2]
Total depreciation, amortization and accretion	1,937		2,178
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	259		259
Provision for uncollectible accounts	16		14
Provision for Obsolete Inventory	7
Stock-based compensation costs	0
Other Decommissioning Related Activity	(110)	[3]	(108)	[3]
Energy-related options	87	[4]	119	[4]
Amortization of debt fair value adjustment	(28)		(23)
Merger related commitments			35	[7]
Severance Costs			34
Gain (loss) on equity method investments	(7)		69
Impairment Of Long Lived Asets Held For Use	149
Amortization of debt costs	7
Other	(5)		23
Total other noncash operating activities	375		422
Changes In Other Assets and Liabilities [Abstract]
Other current assets and liabilities	(123)		(85)
Other noncurrent assets and liabilities	(40)		(110)
Total changes in other assets and liabilities	(163)		(195)
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Merger with Constellation, common stock issued			5,258
Consolidated VIE dividend to non-controlling interest	63
Total noncash investing and financing activities	(63)
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	413		396
Regulatory assets	88		62
Amortization of intangible assets, net			0
Total depreciation, amortization and accretion	501		458
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	231		212
Provision for uncollectible accounts	(6)		38
Stock-based compensation costs	0
Amortization of regulatory asset related to debt costs	7		10
Discrete impacts from EIMA	(206)	[5]	43	[5]
Amortization of debt costs	3		0
Other	(3)		7
Total other noncash operating activities	26		310
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	(63)		21
Other regulatory assets and liabilities	35		65
Other current assets and liabilities	(3)		(8)
Other noncurrent assets and liabilities	261	[8]	(72)
Total changes in other assets and liabilities	160		(124)
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Allocation Of Tax Benefit From Parent	175
Indemnification of like-kind exchange position	0		0
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	164		154
Regulatory assets	7		7
Amortization of intangible assets, net			0
Total depreciation, amortization and accretion	171		161
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	32		38
Provision for uncollectible accounts	48		46
Stock-based compensation costs	0
Amortization of regulatory asset related to debt costs	2		2
Severance Costs			1
Amortization of debt costs	2
Other	0		9
Total other noncash operating activities	84		96
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	(10)		(3)
Other regulatory assets and liabilities	0		(7)
Other current assets and liabilities	(31)		(56)
Other noncurrent assets and liabilities	(6)		(5)
Total changes in other assets and liabilities	(47)		(57)
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures	22		45
Smart Grid Grant Reimbursements	30		55
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	194		184
Regulatory assets	58		34
Amortization of intangible assets, net			0
Total depreciation, amortization and accretion	252		218
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs	41		44
Provision for uncollectible accounts	25		28
Stock-based compensation costs	0
Amortization of regulatory asset related to debt costs	0		1
Amortization of rate stabilization deferral	49		49
Merger related commitments	(6)	[6]	28	[7]
Amortization of debt costs	1
Other	(5)		(2)
Total other noncash operating activities	105		148
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs	26		21
Other regulatory assets and liabilities	85		80
Other current assets and liabilities	(35)		(25)
Other noncurrent assets and liabilities	(25)		7
Total changes in other assets and liabilities	(119)		(77)
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	46		30
Smart Grid Grant Reimbursements	$ 34		$ 30

[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.