Supplemental Financial Information - Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013		Sep. 30, 2014	Sep. 30, 2013
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	$ 55	$ 138	[1]	$ 167	$ 221	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	39	35	[1]	102	65	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	(107)	103		126	196
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	(41)	46		100	70
Net unrealized income (losses) on pledged assets	7	(9)		27	(5)
Regulatory offset to decommissioning trust fund-related activities	29	(189)	[2]	(270)	(338)	[2]
Total decommissioning-related activities	(18)	124		252	209
Investment income	0	1		1	6
Long-term lease income	4	7		20	20
Interest income related to uncertain income tax positions	25			41	24
AFUDC - equity	5	4		17	16
Gain (Loss) on Disposition of Assets	338	10		356	17
Other Income	0	9		15	19
Other, net	354	155		702	311
Exelon Generation Co L L C [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	55	138	[1]	167	221	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	39	35	[1]	102	65	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	(107)	103		126	196
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	(41)	46		100	70
Net unrealized income (losses) on pledged assets	7	(9)		27	(5)
Regulatory offset to decommissioning trust fund-related activities	29	(189)	[2]	(270)	(338)	[2]
Total decommissioning-related activities	(18)	124		252	209
Investment income	0	0		1	(1)
Interest income related to uncertain income tax positions	27			53	3
Gain (Loss) on Disposition of Assets	338	8		355	13
Other Income	(5)	2		0	5
Other, net	342	134		661	229
Commonwealth Edison Co [Member]
Decommissioning-Related Activities [Abstract]
Investment income	0			0
Interest income related to uncertain income tax positions	0			0	0
AFUDC - equity	0	2		3	8
Gain (Loss) on Disposition of Assets	0	2		1	2
Other Income	4	3		10	8
Other, net	4	7		14	18
PECO Energy Co [Member]
Decommissioning-Related Activities [Abstract]
Investment income	0	0		(1)	(1)
Interest income related to uncertain income tax positions	0			0	1
AFUDC - equity	2	1		5	3
Gain (Loss) on Disposition of Assets	0	0		0	0
Other Income	0	0		1	1
Other, net	2	1		5	4
Baltimore Gas and Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income	1	2	[3]	5	7	[3]
Interest income related to uncertain income tax positions	0			0
AFUDC - equity	3	1		9	5
Gain (Loss) on Disposition of Assets	0	0		0	0
Other Income	0	1		0	1
Other, net	$ 4	$ 4		$ 14	$ 13

[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 2013 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

[3] Relates to the cash return on BGE’s rate stabilization deferral. See Note 5 — Regulatory Matters for additional information regarding the rate stabilization deferral.