Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015		Jun. 30, 2014
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment				$ 1,087		$ 1,015
Regulatory assets				101		117
Amortization of intangible assets, net				24		22
Amortization of energy contract assets and liabilities	[1]			0		113
Nuclear fuel	[2]			552		499
Asset retirement obligation accretion	[3]			193		159
Total depreciation, amortization and accretion				1,957		1,925
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				317		315
Gain (loss) on equity method investments		$ 0	$ 0	2		20
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions		2	0	2		0
Provision for uncollectible accounts				80		59
Stock-based compensation costs				79		68
Other Decommissioning Related Activity	[4]			(50)		(85)
Energy-related options				27	[5]	63
Amortization of regulatory asset related to debt costs				0
Amortization of rate stabilization deferral				40		33
Amortization of debt fair value adjustment				37		26
Discrete impacts from EIMA	[6]			77		9
Amortization of debt costs				35		19
Inventory Write-down				13
Tangible Asset Impairment Charges		24
Other				(4)		(2)
Total other noncash operating activities				579		473
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs				45		60
Other regulatory assets and liabilities				47		(25)
Increase (Decrease) in Deposits	[7]			242
Increase (Decrease) in Other Current Liabilities				(53)
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net				67
Other current assets and liabilities						(157)
Other noncurrent assets and liabilities						(158)
Total changes in other assets and liabilities				214		(280)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						3,400
Non Cash Licensing Agreement				95
Consolidated VIE dividend to non-controlling interest				0		(415)
Total noncash investing and financing activities				95		3,569
Indemnification Agreement [Member]
Other Non-Cash Operating Activities [Abstract]
Energy-related options						38
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment				485		444
Regulatory assets				0		0
Amortization of intangible assets, net				24		22
Amortization of energy contract assets and liabilities	[1]			1		118
Nuclear fuel	[2]			552		499
Asset retirement obligation accretion	[3]			193		159
Total depreciation, amortization and accretion				1,255		1,242
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				133		139
Gain (loss) on equity method investments			1	3		20
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions		$ 2		3
Provision for uncollectible accounts				11		8
Stock-based compensation costs				0		0
Other Decommissioning Related Activity	[4]			(50)		(85)
Energy-related options	[5]			27		63
Amortization of regulatory asset related to debt costs				0
Amortization of rate stabilization deferral				0		0
Amortization of debt fair value adjustment				6		12
Discrete impacts from EIMA				0		0
Amortization of debt costs				8		6
Inventory Write-down				13
Tangible Asset Impairment Charges			$ 86
Other				(5)		0
Total other noncash operating activities				134		139
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	[7]			242
Increase (Decrease) in Other Current Liabilities				(39)
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net				0
Other current assets and liabilities						13
Other noncurrent assets and liabilities						(69)
Total changes in other assets and liabilities				203		(56)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Non cash Fair Value Adjustment for CENG						3,400
Consolidated VIE dividend to non-controlling interest				0		(415)
Total noncash investing and financing activities				0		3,438
Exelon Generation Co L L C [Member] | Indemnification Agreement [Member]
Other Non-Cash Operating Activities [Abstract]
Energy-related options						38
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment				312		290
Regulatory assets				40		57
Total depreciation, amortization and accretion				352		347
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				103		96
Provision for uncollectible accounts				35		(8)
Stock-based compensation costs				0
Energy-related options	[5]					0
Amortization of regulatory asset related to debt costs				0
Discrete impacts from EIMA	[6]			77		9
Amortization of debt costs				2		(3)
Inventory Write-down				0
Other				5		5
Total other noncash operating activities				222		99
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs				10		61
Other regulatory assets and liabilities				26		(30)
Increase (Decrease) in Deposits				0
Increase (Decrease) in Other Current Liabilities				3
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net				14
Other current assets and liabilities						(5)
Other noncurrent assets and liabilities						22
Total changes in other assets and liabilities				25		48
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position				45		112
Total noncash investing and financing activities				3		2
Commonwealth Edison Co [Member] | Indemnification Agreement [Member]
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Indemnification of like-kind exchange position	[8]			3		2
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment				119		112
Regulatory assets				12		5
Total depreciation, amortization and accretion				131		117
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				19		21
Gain (loss) on equity method investments						0
Provision for uncollectible accounts				24		28
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						0
Amortization of debt fair value adjustment						0
Discrete impacts from EIMA						0
Amortization of debt costs				1		1
Inventory Write-down				0
Other				1		0
Total other noncash operating activities				45		50
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs				27		(6)
Other regulatory assets and liabilities				(13)		(13)
Increase (Decrease) in Deposits				0
Increase (Decrease) in Other Current Liabilities	[9]			(74)
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net				0
Other current assets and liabilities	[9]					(89)
Other noncurrent assets and liabilities						(6)
Total changes in other assets and liabilities				(60)		(114)
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment				143		142
Regulatory assets				49		55
Total depreciation, amortization and accretion				192		197
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefit Expense				33		33
Gain (loss) on equity method investments						0
Provision for uncollectible accounts				11		30
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				40		33
Amortization of debt fair value adjustment						0
Discrete impacts from EIMA						0
Amortization of debt costs				1		1
Inventory Write-down				0
Other				(9)		(8)
Total other noncash operating activities				76		89
Changes In Other Assets and Liabilities [Abstract]
Under/over-recovered energy and transmission costs				8		8
Other regulatory assets and liabilities				(18)		(49)
Increase (Decrease) in Deposits				0
Increase (Decrease) in Other Current Liabilities				60
Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net				(1)
Other current assets and liabilities						51
Other noncurrent assets and liabilities						(2)
Total changes in other assets and liabilities				51		$ 8
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 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 recalled from ISOs/RTOs and replaced with letters of credit.

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

[9] Relates primarily to prepaid utility taxes.