Supplemental Financial Information - Cash Flow (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			$ 1,549		$ 1,420
Regulatory assets			150		153
Amortization of intangible assets, net			33		33
Amortization of energy contract assets and liabilities			83	[1]	342	[1]
Nuclear fuel			790	[2]	689	[2]
Asset retirement obligation accretion			251	[3]	207	[3]
Total depreciation, amortization and accretion			2,856		2,844
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs			437		621
Gain (loss) on equity method investments	(1)	(37)	20		(7)
Provision for uncollectible accounts			96		83
Stock-based compensation costs			111		99
Other Decommissioning Related Activity			(102)	[4]	(110)	[4]
Energy-related options			92	[5]	87	[5]
Amortization of regulatory asset related to debt costs			8		9
Amortization of rate stabilization deferral			50		49
Amortization of debt fair value adjustment			(45)		(28)
Discrete impacts from EIMA			(32)	[6]	(206)	[6]
Amortization of debt costs			36		13
Merger related commitments			44		(6)	[7]
Inventory Write-down					7
Other			(17)		(27)
Total other noncash operating activities			698		584
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs			53		(47)
Other regulatory assets and liabilities			(63)		(50)
Increase (Decrease) in Deposits			(280)	[8]
Increase (Decrease) in Other Current Liabilities			(78)
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net			168
Increase (Decrease) in Other Noncurrent Liabilities					26	[9]
Other current assets and liabilities					(169)
Other noncurrent assets and liabilities					205
Total changes in other assets and liabilities			(536)		(35)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG			(3,400)	[10]
Debt exchange			131	[11]
Non Cash Debt Instrument Issued			70	[12]
Consolidated VIE dividend to non-controlling interest			(415)		0
Total noncash investing and financing activities			(3,199)		63
Indemnification Agreement [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Consolidated VIE dividend to non-controlling interest					63
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			686		610
Amortization of intangible assets, net			33		33
Amortization of energy contract assets and liabilities			93	[1]	398	[1]
Nuclear fuel			790	[2]	689	[2]
Asset retirement obligation accretion			251	[3]	207	[3]
Total depreciation, amortization and accretion			1,853		1,937
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs			193		259
Gain (loss) on equity method investments	(1)	(37)	20		(7)
Provision for uncollectible accounts			10		16
Stock-based compensation costs					0
Other Decommissioning Related Activity			(102)	[4]	(110)	[4]
Energy-related options			92	[5]	87	[5]
Amortization of regulatory asset related to debt costs					0
Amortization of rate stabilization deferral					0
Amortization of debt fair value adjustment			(17)		(28)
Discrete impacts from EIMA					0	[6]
Amortization of debt costs			9		7
Merger related commitments			44		0	[7]
Inventory Write-down					7
Other			2		0
Total other noncash operating activities			251		231
Changes In Other Assets and Liabilities [Abstract]
Increase (Decrease) in Deposits			(280)	[8]
Increase (Decrease) in Other Current Liabilities			24
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net			111
Other current assets and liabilities					(123)
Other noncurrent assets and liabilities					(40)
Total changes in other assets and liabilities			(367)		(163)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG			(3,400)	[10]
Non Cash Debt Instrument Issued			70	[12]
Consolidated VIE dividend to non-controlling interest			(415)		0
Total noncash investing and financing activities			(3,330)		63
Exelon Generation Co L L C [Member] | Indemnification Agreement [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Consolidated VIE dividend to non-controlling interest					63
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			438		413
Regulatory assets			83		88
Total depreciation, amortization and accretion			521		501
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs			129		231
Provision for uncollectible accounts			9		(6)
Stock-based compensation costs			0
Energy-related options					0	[5]
Amortization of regulatory asset related to debt costs			6		7
Discrete impacts from EIMA			(32)	[6]	(206)	[6]
Amortization of debt costs			4		3
Other			0		(3)
Total other noncash operating activities			116		26
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs			63		(63)
Other regulatory assets and liabilities			(14)		(35)
Increase (Decrease) in Deposits			0	[8]
Increase (Decrease) in Other Current Liabilities			(9)
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net			(22)
Other current assets and liabilities					47
Other noncurrent assets and liabilities					261	[13]
Total changes in other assets and liabilities			62		210
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position			168		0
Total noncash investing and financing activities			4		175
Commonwealth Edison Co [Member] | Indemnification Agreement [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position			4	[14]	175	[10]
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			169		164
Regulatory assets			7		7
Total depreciation, amortization and accretion			176		171
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs			28		32
Gain (loss) on equity method investments					0
Provision for uncollectible accounts			39		48
Stock-based compensation costs			0		0
Other Decommissioning Related Activity					0	[4]
Energy-related options					0	[5]
Amortization of regulatory asset related to debt costs			2		2
Amortization of rate stabilization deferral					0
Amortization of debt fair value adjustment					0
Discrete impacts from EIMA					0	[6]
Amortization of debt costs			2		2
Merger related commitments					0	[7]
Other			(1)		0
Total other noncash operating activities			70		84
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs			(14)		(10)
Other regulatory assets and liabilities			(14)		0
Increase (Decrease) in Deposits			0	[8]
Increase (Decrease) in Other Current Liabilities			(48)	[15]
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net			(1)
Other current assets and liabilities					(31)	[15]
Other noncurrent assets and liabilities					(6)
Total changes in other assets and liabilities			(75)		(47)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position			24		0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			215		194
Regulatory assets			60		58
Total depreciation, amortization and accretion			275		252
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefits costs			50		41
Gain (loss) on equity method investments					0
Provision for uncollectible accounts			38		25
Stock-based compensation costs			0		0
Other Decommissioning Related Activity					0	[4]
Energy-related options					0	[5]
Amortization of regulatory asset related to debt costs			0		0
Amortization of rate stabilization deferral			50		49
Amortization of debt fair value adjustment					0
Discrete impacts from EIMA					0	[6]
Amortization of debt costs			2		1
Merger related commitments					(6)	[7]
Other			(11)		(5)
Total other noncash operating activities			129		105
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs			6		26
Other regulatory assets and liabilities			(89)		(85)
Increase (Decrease) in Deposits			0	[8]
Increase (Decrease) in Other Current Liabilities			25
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net			9
Other current assets and liabilities					(35)
Other noncurrent assets and liabilities					(25)
Total changes in other assets and liabilities			(67)		(119)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position			$ 0

[1] Included in Operating revenues or Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[2] Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[3] Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[4] 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 of the Exelon 2013 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

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

[6] 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.

[7] Relates to integration costs to achieve distribution synergies related to the Constellation merger transaction that were reclassified to a regulatory asset. See Note 5 — Regulatory Matters for more information.

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

[9] Relates to settlement of forward starting interest rate swaps that Exelon entered into in anticipation of Continental Wind, LLC non-recourse project financing that was completed on September 30, 2013. See Note 9 — Derivative Financial Instruments for more information on interest rate swaps.

[10] See Note 6 — Investment in Constellation Energy Nuclear Group, LLC for additional information.

[11] Relates to the present value of the contract payments for the equity units issued by Exelon. See Note 16 — Common Stock for additional information.

[12] 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.

[13] Relates primarily to interest payable related to like-kind exchange tax position. See Note 11 — Income Taxes for discussion of the like-kind exchange tax position.

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

[15] Relates primarily to prepaid utility taxes.