Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment				$ 1,648		$ 1,549
Regulatory assets				131		150
Amortization of intangible assets, net				39		33
Amortization of energy contract assets and liabilities	[1]			(20)		83
Nuclear fuel	[2]			841		790
Asset retirement obligation accretion	[3]			291		251
Total depreciation, amortization and accretion				2,930		2,856
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				476		437
Gain (loss) on equity method investments			$ 0	3		20
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions		$ 1		3
Provision for uncollectible accounts				114		96
Stock-based compensation costs				102		111
Other Decommissioning Related Activity	[4]			(31)		(102)
Energy-related options				18	[5]	92
Amortization of regulatory asset related to debt costs						8
Amortization of rate stabilization deferral				60		50
Amortization of debt fair value adjustment				34		45
Discrete impacts from EIMA	[6]			101		(32)
Amortization of debt costs				43		36
Non Cash Increase in Inventory Reserve				7
Merger related commitments						44
Inventory Write-down				15
Tangible Asset Impairment Charges		24
Other Noncash Income Expense Net				(18)		(17)
Total other noncash operating activities				856		698
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs				47		53
Other regulatory assets and liabilities				(12)		(63)
Increase (Decrease) in Deposits				(190)	[7]	(280)
Increase (Decrease) in Other Current Liabilities				(132)
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net				193
Other current assets and liabilities						(78)
Other noncurrent assets and liabilities						(168)
Total changes in other assets and liabilities				(480)		(536)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						3,400
Capital Expenditures Incurred but Not yet Paid				59		(73)
Non Cash Licensing Agreement				95
Consolidated VIE dividend to non-controlling interest				0
Costs Incurred, Asset Retirement Obligation Incurred				(811)		(91)
Stock Issued						131
Indemnification Agreement [Member]
Other Non-Cash Operating Activities [Abstract]
Energy-related options						70
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment				739		686
Regulatory assets				0		0
Amortization of intangible assets, net				35		33
Amortization of energy contract assets and liabilities	[1]			(19)		93
Nuclear fuel	[2]			841		790
Asset retirement obligation accretion	[3]			291		251
Total depreciation, amortization and accretion				1,887		1,853
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				200		193
Gain (loss) on equity method investments			(1)	4		20
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions		$ 1		4
Provision for uncollectible accounts				15		10
Stock-based compensation costs				0		0
Other Decommissioning Related Activity	[4]			(31)		(102)
Energy-related options	[5]			18		92
Amortization of regulatory asset related to debt costs						0
Amortization of rate stabilization deferral				0		0
Amortization of debt fair value adjustment				9		17
Discrete impacts from EIMA				0		0
Amortization of debt costs				12		9
Non Cash Increase in Inventory Reserve				8
Merger related commitments						44
Inventory Write-down				15
Tangible Asset Impairment Charges			$ 86
Other Noncash Income Expense Net				(5)		2
Total other noncash operating activities				227		251
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs				0
Other regulatory assets and liabilities				0
Increase (Decrease) in Deposits				(190)	[7]	(280)
Increase (Decrease) in Other Current Liabilities				(143)
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net				92
Other current assets and liabilities						24
Other noncurrent assets and liabilities						(111)
Total changes in other assets and liabilities				(425)		(367)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						3,400
Capital Expenditures Incurred but Not yet Paid				48		(100)
Consolidated VIE dividend to non-controlling interest				0
Costs Incurred, Asset Retirement Obligation Incurred				(811)		(91)
Exelon Generation Co L L C [Member] | Indemnification Agreement [Member]
Other Non-Cash Operating Activities [Abstract]
Energy-related options						70
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment				471		438
Regulatory assets				57		83
Total depreciation, amortization and accretion				528		521
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				155		129
Provision for uncollectible accounts				46		9
Stock-based compensation costs				0
Energy-related options	[5]					0
Amortization of regulatory asset related to debt costs						0
Discrete impacts from EIMA	[6]			101		(32)
Amortization of debt costs				3		4
Inventory Write-down				0
Other Noncash Income Expense Net				7		6
Total other noncash operating activities				312		116
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs				27		63
Other regulatory assets and liabilities				29		(14)
Increase (Decrease) in Deposits				0
Increase (Decrease) in Other Current Liabilities				2
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net				65
Other current assets and liabilities						(9)
Other noncurrent assets and liabilities						22
Total changes in other assets and liabilities				(7)		62
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid				62		13
Indemnification of like-kind exchange position				75		168
Commonwealth Edison Co [Member] | Indemnification Agreement [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position	[8]			5		4
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment				179		169
Regulatory assets				19		7
Amortization of intangible assets, net				0		0
Amortization of energy contract assets and liabilities	[1]			0		0
Nuclear fuel	[2]			0		0
Asset retirement obligation accretion	[3]			0		0
Total depreciation, amortization and accretion				198		176
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				29		28
Gain (loss) on equity method investments				0		0
Provision for uncollectible accounts				37		39
Stock-based compensation costs				0		0
Other Decommissioning Related Activity				0	[4]	0
Energy-related options	[5]			0		0
Amortization of regulatory asset related to debt costs						0
Amortization of rate stabilization deferral				0		0
Amortization of debt fair value adjustment				0		0
Discrete impacts from EIMA				0		0
Amortization of debt costs				2		2
Merger related commitments						0
Inventory Write-down				0
Other Noncash Income Expense Net				1		1
Total other noncash operating activities				69		70
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs				12		(14)
Other regulatory assets and liabilities				(4)		(14)
Increase (Decrease) in Deposits				0		0
Increase (Decrease) in Other Current Liabilities	[9]			(23)
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net				3
Other current assets and liabilities	[9]					(48)
Other noncurrent assets and liabilities						1
Total changes in other assets and liabilities				(18)		(75)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						0
Capital Expenditures Incurred but Not yet Paid				23		(13)
PECO Energy Co [Member] | Indemnification Agreement [Member]
Other Non-Cash Operating Activities [Abstract]
Energy-related options						0
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position	[8]			0		0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment				216		215
Regulatory assets				55		60
Total depreciation, amortization and accretion				271		275
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				49		50
Gain (loss) on equity method investments						0
Provision for uncollectible accounts				15		38
Stock-based compensation costs				0		0
Other Decommissioning Related Activity						0
Energy-related options	[5]					0
Amortization of regulatory asset related to debt costs						0
Amortization of rate stabilization deferral				60		50
Amortization of debt fair value adjustment						0
Discrete impacts from EIMA						0
Amortization of debt costs				2		2
Merger related commitments						0
Inventory Write-down				0
Other Noncash Income Expense Net				(15)		(11)
Total other noncash operating activities				111		129
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs				8		6
Other regulatory assets and liabilities				(106)		(89)
Increase (Decrease) in Deposits				0
Increase (Decrease) in Other Current Liabilities				55
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net				0
Other current assets and liabilities						25
Other noncurrent assets and liabilities						(9)
Total changes in other assets and liabilities				(43)		(67)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid				14		$ 31
Indemnification of like-kind exchange position				$ 6

[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 2014 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 primarily to cash deposits made to ISOs/RTOs.

[8] See Note 12 — Income Taxes for discussion of the like-kind exchange tax position

[9] Relates primarily to prepaid utility taxes.