Supplemental Financial Information - Operations (Detail) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2015		Jun. 30, 2014		Jun. 30, 2015		Jun. 30, 2014
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	$ 93		$ 68		$ 164		$ 111
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	74		38		104		63
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		(133)		172		(85)		234
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		(96)		128		(56)		141
Net unrealized income (losses) on pledged assets				10		9		20
Regulatory offset to decommissioning trust fund-related activities	[2]	28		(204)		(78)		(299)
Total decommissioning-related activities		(34)		212		58		270
Investment income		1		7		4		8
Long-term lease income		4		10		8		17
Interest income related to uncertain income tax positions				(2)		0		7
AFUDC - equity		5		4		11		12
Gain (Loss) on Sale of Derivatives	[3]					(26)
Other Income		7		(1)		9		16
Other, net		(17)		230		64		330
Exelon Generation Co L L C [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	93		68		164		111
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	74		38		104		63
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		(133)		172		(85)		234
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		(96)		128		(56)		141
Net unrealized income (losses) on pledged assets				10		9		20
Regulatory offset to decommissioning trust fund-related activities	[2]	28		(204)		(78)		(299)
Total decommissioning-related activities		(34)		212		58		270
Investment income		0		7		1		8
Long-term lease income		0		0		0		0
Interest income related to uncertain income tax positions				3		1		17
AFUDC - equity						0		0
Gain (Loss) on Sale of Derivatives	[3]					0
Other Income		3		(6)		2		5
Other, net		(31)		216		62		300
Commonwealth Edison Co [Member]
Decommissioning-Related Activities [Abstract]
Investment income		0				0
Interest income related to uncertain income tax positions						0		0
AFUDC - equity		1		0		1		3
Other Income		4		5		8		7
Other, net		5		5		9		10
PECO Energy Co [Member]
Decommissioning-Related Activities [Abstract]
Investment income		(1)		(1)		(1)		(1)
Interest income related to uncertain income tax positions						0		0
AFUDC - equity		1		1		3		3
Gain (Loss) on Disposition of Assets						1
Other Income		1		1		1		1
Other, net		1		1		3		3
Baltimore Gas and Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income		1	[4]	2	[4]	2	[4]	4
Long-term lease income								0
Interest income related to uncertain income tax positions						0		0
AFUDC - equity		3		3		7		6
Other Income		0		0		(1)		(1)
Other, net		$ 4		$ 5		8		$ 9
Reclassification out of Accumulated Other Comprehensive Income [Member]
Decommissioning-Related Activities [Abstract]
Gain (Loss) on Sale of Derivatives	[3]					$ 26

[1] Includes investment income and realized gains and losses on sales of investments of the trust funds.

[2] Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 15 — Asset Retirement Obligations of the Exelon 2014 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

[3] In January 2015, in connection with Generation's $750 million issuance of five-year Senior Unsecured Notes, Exelon terminated certain floating-to-fixed interest rate swaps. As the original forecasted transactions were a series of future interest payments over a ten year period, a portion of the anticipated interest payments are probable not to occur. As a result, $26 million of anticipated payments were reclassified from Accumulated OCI to Other, net in Exelon's Consolidated Statement of Operations and Comprehensive Income.

[4] Relates to the cash return on BGE’s rate stabilization deferral. See Note 3 — Regulatory Matters of the Exelon 2014 Form 10-K for additional information regarding the rate stabilization deferral.