Supplemental Financial Information - Cash Flow (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			$ 1,015		$ 942
Regulatory assets			117		112
Amortization of intangible assets, net			22		22
Amortization of energy contract assets and liabilities			113	[1]	306	[1]
Nuclear fuel			499	[1]	454	[1]
Asset retirement obligation accretion			159	[2]	136	[2]
Total depreciation, amortization and accretion			1,925		1,972
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs			315		409
Provision for uncollectible accounts			59		55
Provision for Obsolete Inventory			3
Stock-based compensation costs			68		70
Other Decommissioning Related Activity			(85)	[3]	(62)	[3]
Energy-related options			63	[4]	65	[4]
Amortization of regulatory asset related to debt costs			5		6
Amortization of rate stabilization deferral			33		29
Amortization of debt fair value adjustment			(26)		(22)
Discrete impacts from EIMA			9		(126)	[5]
Merger related commitments					(6)
Gain (loss) on equity method investments	0	21	20		30
Impairment in investment of direct financing leases			24
Impairment Of Long Lived Asets Held For Use			86
Amortization of debt costs			19		8
Other			(26)		(17)
Total other noncash operating activities			567		576
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs			60		(24)
Other regulatory assets and liabilities			25		(3)
Other current assets and liabilities			(157)		(123)
Other noncurrent assets and liabilities			(158)		277
Total changes in other assets and liabilities			(280)		133
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Debt exchange			131
Consolidated VIE dividend to non-controlling interest			(415)		63
Non Cash Fair Value Adjust for CENG			3,400
Non Cash Debt Instrument Issued			38
Total noncash investing and financing activities			(3,569)		63
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures			2		41
Smart Grid Grant Reimbursements			3		50
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			444		402
Regulatory assets					0
Amortization of intangible assets, net			22		22
Amortization of energy contract assets and liabilities			118	[1]	344	[1]
Nuclear fuel			499	[1]	454	[1]
Asset retirement obligation accretion			159	[2]	136	[2]
Total depreciation, amortization and accretion			1,242		1,358
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs			139		173
Provision for uncollectible accounts			8		10
Provision for Obsolete Inventory			3
Stock-based compensation costs			0		0
Other Decommissioning Related Activity			(85)	[3]	(62)	[3]
Energy-related options			63	[4]	65	[4]
Amortization of debt fair value adjustment			(12)		(22)
Merger related commitments					0
Gain (loss) on equity method investments	1	21	20		30
Impairment Of Long Lived Asets Held For Use			86
Amortization of debt costs			6		5
Other			(19)		(7)
Total other noncash operating activities			209		315
Changes In Other Assets and Liabilities [Abstract]
Other current assets and liabilities			13		(134)
Other noncurrent assets and liabilities			(69)		(34)
Total changes in other assets and liabilities			(56)		(168)
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Consolidated VIE dividend to non-controlling interest			(415)		63
Non Cash Fair Value Adjust for CENG			3,400
Non Cash Debt Instrument Issued			38
Total noncash investing and financing activities			(3,438)		63
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			290		275
Regulatory assets			57		62
Amortization of intangible assets, net					0
Total depreciation, amortization and accretion			347		337
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs			96		154
Provision for uncollectible accounts			(8)		4
Provision for Obsolete Inventory			1
Stock-based compensation costs			0		0
Amortization of regulatory asset related to debt costs			4		5
Discrete impacts from EIMA			9		(126)	[5]
Amortization of debt costs			(3)		2
Other			0		0
Total other noncash operating activities			99		39
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs			61		(61)
Other regulatory assets and liabilities			30		28
Other current assets and liabilities			(5)		2
Other noncurrent assets and liabilities			22		304
Total changes in other assets and liabilities			48		217
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Allocation Of Tax Benefit From Parent			2
Indemnification of like-kind exchange position			(112)		0
Total noncash investing and financing activities			(2)		174
Commonwealth Edison Co [Member] | Indemnification Agreement [Member]
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position			2		(174)
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			112		109
Regulatory assets			5		4
Amortization of intangible assets, net					0
Total depreciation, amortization and accretion			117		113
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs			21		21
Provision for uncollectible accounts			28		27
Stock-based compensation costs			0		0
Amortization of regulatory asset related to debt costs			1		1
Amortization of debt costs			1		1
Other			(1)		0
Total other noncash operating activities			50		50
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs			(6)		19
Other regulatory assets and liabilities			13		5
Other current assets and liabilities			(89)		(62)
Other noncurrent assets and liabilities			(6)		(1)
Total changes in other assets and liabilities			(114)		(49)
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures			2		12
Smart Grid Grant Reimbursements			3		16
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			142		128
Regulatory assets			55		47
Amortization of intangible assets, net					0
Total depreciation, amortization and accretion			197		175
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs			33		27
Provision for uncollectible accounts			30		14
Stock-based compensation costs			0		0
Amortization of regulatory asset related to debt costs			0		0
Amortization of rate stabilization deferral			33		29
Merger related commitments					(6)
Amortization of debt costs			1
Other			(8)		(3)
Total other noncash operating activities			89		61
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs			8		18
Other regulatory assets and liabilities			49		82
Other current assets and liabilities			51		99
Other noncurrent assets and liabilities			(2)		28
Total changes in other assets and liabilities			8		63
Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position			0		0
DOE Smart Grid Investment Grant [Abstract]
Amount included in capital expenditures					29
Smart Grid Grant Reimbursements					$ 34

[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 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 of the Exelon 2013 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.