Supplemental Financial Information - Operations (Detail) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2015		Sep. 30, 2014		Sep. 30, 2015		Sep. 30, 2014
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	$ 39		$ 55		$ 203		$ 167
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	18		39		122		102
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		(301)		(107)		(385)		126
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		(218)		(41)		(274)		100
Net unrealized income (losses) on pledged assets				7		9		27
Regulatory offset to decommissioning trust fund-related activities	[2]	207		29		129		(270)
Total decommissioning-related activities		(255)		(18)		(196)		252
Investment income		4		0		6		1
Long-term lease income		4		4		12		20
Interest income related to uncertain income tax positions				25		0		41
AFUDC - equity		6		5		16		17
Gain (Loss) on Sale of Derivatives	[3]					(26)
Other Income		(3)		0		9		15
Other, net		(244)		16		(179)		346
Exelon Generation Co L L C [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	39		55		203		167
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	18		39		122		102
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		(301)		(107)		(385)		126
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		(218)		(41)		(274)		100
Net unrealized income (losses) on pledged assets				7		9		27
Regulatory offset to decommissioning trust fund-related activities	[2]	207		29		129		(270)
Total decommissioning-related activities		(255)		(18)		(196)		252
Investment income		1		0		1		1
Long-term lease income		0		0		0		0
Interest income related to uncertain income tax positions				27		1		53
AFUDC - equity						0		0
Gain (Loss) on Sale of Derivatives	[3]					0
Other Income		(3)		(5)		1		0
Other, net		(257)		4		(193)		306
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		2		3
Other Income		3		4		12		11
Other, net		4		4		14		14
PECO Energy Co [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	0		0		0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	0		0		0		0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0		0		0		0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0		0		0		0
Net unrealized income (losses) on pledged assets				0		0		0
Regulatory offset to decommissioning trust fund-related activities	[2]	0		0		0		0
Total decommissioning-related activities		0		0		0		0
Investment income		(1)		0		(1)		(1)
Long-term lease income		0		0		0		0
Interest income related to uncertain income tax positions						0		0
AFUDC - equity		1		2		4		5
Gain (Loss) on Disposition of Assets		0		0		1
Gain (Loss) on Sale of Derivatives	[3]					0
Other Income		1		0		0		1
Other, net		1		2		3		5
Baltimore Gas and Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income		1	[4]	1	[4]	3	[4]	5
Long-term lease income								0
Interest income related to uncertain income tax positions						0		0
AFUDC - equity		4		3		10		9
Gain (Loss) on Disposition of Assets		1				1
Other Income		(1)		0		0		0
Other, net		$ 4		$ 4		13		$ 14
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.