Supplemental Financial Information - Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	$ 71		$ 43	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	29		25	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	48		61
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	40		13
Net unrealized income (losses) on pledged assets	10		10
Regulatory offset to decommissioning trust fund-related activities	(106)	[2]	(94)	[2]
Total decommissioning-related activities	92		58
Investment income	1		1
Long-term lease income	4		6
Interest income related to uncertain income tax positions	0		10
AFUDC - equity	5		6
Gain (Loss) on Sale of Derivatives	(23)	[3]
Other Income	1		17
Other, net	80		98
Exelon Generation Co L L C [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	71		43	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	29		25	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	48		61
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	40		13
Net unrealized income (losses) on pledged assets	10		10
Regulatory offset to decommissioning trust fund-related activities	(106)	[2]	(94)	[2]
Total decommissioning-related activities	92		58
Investment income	1		1
Long-term lease income	0		0
Interest income related to uncertain income tax positions	1		14
AFUDC - equity	0		0
Gain (Loss) on Sale of Derivatives	3	[3]
Other Income	(3)		12
Other, net	94		85
Commonwealth Edison Co [Member]
Decommissioning-Related Activities [Abstract]
Investment income	0
Interest income related to uncertain income tax positions	0		0
AFUDC - equity	0		3
Other Income	3		2
Other, net	3		5
PECO Energy Co [Member]
Decommissioning-Related Activities [Abstract]
Investment income	0		0
Interest income related to uncertain income tax positions	0		0
AFUDC - equity	2		1
Other Income	0		1
Other, net	2		2
Baltimore Gas and Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income	1	[4]
Interest income related to uncertain income tax positions	0
AFUDC - equity	3
Other Income	0
Other, net	$ 4		$ 4

[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.