Supplemental Financial Information - Summary of Other Income (Expense) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	$ 216	[1]	$ 256	[1]	$ 189	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	159	[1]	77	[1]	102	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	180	[1]	406	[1]	386	[1]
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	134	[1]	146	[1]	105	[1]
Net unrealized income (losses) on pledged assets	29	[1]	7	[1]	73	[1]
Regulatory offset to decommissioning trust fund-related activities	(358)	[1],[2]	(546)	[1],[2]	(530)	[1],[2]
Total decommissioning-related activities	360		346		325
Investment income	1		8		20
Long-term lease income	24		28		29
Interest income related to uncertain income tax positions	40		24		15
AFUDC—Equity	21		22		17
Credit facility termination fees					(85)
Other	9		32		32
Other, net	455		460		353
Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	216	[1]	256	[1]	189	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	159	[1]	77	[1]	102	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	180	[1]	406	[1]	386	[1]
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	134	[1]	146	[1]	105	[1]
Net unrealized income (losses) on pledged assets	29	[1]	7	[1]	73	[1]
Regulatory offset to decommissioning trust fund-related activities	(358)	[1],[2]	(546)	[1],[2]	(530)	[1],[2]
Total decommissioning-related activities	360		346		325
Investment income	1		(1)		3
Long-term lease income	0		0		0
Interest income related to uncertain income tax positions	54		4		2
AFUDC—Equity	0		0		0
Credit facility termination fees					(85)
Other	(9)		6		1
Other, net	406		355		246
Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	0	[1]	0	[1]	0	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	0	[1]	0	[1]	0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	0	[1]	0	[1]	0	[1]
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	0	[1]	0	[1]	0	[1]
Net unrealized income (losses) on pledged assets	0	[1]	0	[1]	0	[1]
Regulatory offset to decommissioning trust fund-related activities	0	[1],[2]	0	[1],[2]	0	[1],[2]
Total decommissioning-related activities	0		0		0
Investment income	0		0		1
Long-term lease income	0		0		0
Interest income related to uncertain income tax positions	0		0		20
AFUDC—Equity	3		11		6
Credit facility termination fees					0
Other	14		15		12
Other, net	17		26		39
Other Income	17
PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	0	[1]	0	[1]	0	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	0	[1]	0	[1]	0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	0	[1]	0	[1]	0	[1]
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	0	[1]	0	[1]	0	[1]
Net unrealized income (losses) on pledged assets	0	[1]	0	[1]	0	[1]
Regulatory offset to decommissioning trust fund-related activities	0	[1],[2]	0	[1],[2]	0	[1],[2]
Total decommissioning-related activities	0		0		0
Investment income	(1)		(1)		2
Long-term lease income	0		0		0
Interest income related to uncertain income tax positions	0		0		0
AFUDC—Equity	6		4		4
Credit facility termination fees					0
Other	2		3		2
Other, net	7		6		8
Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	0	[1]	0	[1]	0	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	0	[1]	0	[1]	0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	0	[1]	0	[1]	0	[1]
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	0	[1]	0	[1]	0	[1]
Net unrealized income (losses) on pledged assets	0	[1]	0	[1]	0	[1]
Regulatory offset to decommissioning trust fund-related activities	0	[1],[2]	0	[1],[2]	0	[1],[2]
Total decommissioning-related activities	0		0		0
Investment income	7	[3]	9	[3]	11	[3]
Long-term lease income	0		0		0
Interest income related to uncertain income tax positions	0		0		0
AFUDC—Equity	12		7		10
Credit facility termination fees					0
Other	(1)		1		2
Other, net	$ 18		$ 17		$ 23

[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 for additional information regarding the accounting for nuclear decommissioning.

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