Regulatory Matters Regulatory Matters - Schedule of Regulatory Liabilities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Regulatory Liabilities [Line Items]
Current	$ 364		$ 327
Noncurrent	4,593		4,388
Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Current	53		2
Noncurrent	96		43
Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	2,850		2,740
Removal Costs [Member]
Regulatory Liabilities [Line Items]
Current	110		99
Noncurrent	1,455		1,423
Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Current	28		53
Noncurrent	2		0
Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Current	0		1
Noncurrent	10		10
Energy Efficiency Phase [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	32		21
Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Current	20		20
Noncurrent	100		114
Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Current	8		8
Noncurrent	32		37
Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Current	73		78
Noncurrent	13		0
Over-Recovered Universal Service Fund Costs [Member]
Regulatory Liabilities [Line Items]
Current	4		8
Noncurrent	0		0
Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Current	47	[1]	38	[1]
Noncurrent	0	[1]	0	[1]
Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Current	16	[2]	16	[2]
Noncurrent	0	[2]	0	[2]
Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Current	5		4
Noncurrent	3		0
Transmission Rate Formula [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3
Over-Recovered Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3		11
Under-Recovered Electric Supply Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities			1
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities [Line Items]
Current	45		48
Noncurrent	199		204
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Gas Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	16		9
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Electric Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities			7
Baltimore Gas and Electric Company [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
Baltimore Gas and Electric Company [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
Baltimore Gas and Electric Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Current	24		21
Noncurrent	198		204
Baltimore Gas and Electric Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
Baltimore Gas and Electric Company [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
Baltimore Gas and Electric Company [Member] | Energy Efficiency Phase [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
Baltimore Gas and Electric Company [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
Baltimore Gas and Electric Company [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Current	0
Noncurrent	0
Baltimore Gas and Electric Company [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Current	3	[3]	11	[3]
Noncurrent	0		0
Baltimore Gas and Electric Company [Member] | Over-Recovered Universal Service Fund Costs [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
Baltimore Gas and Electric Company [Member] | Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Current	0	[1]	0	[1]
Noncurrent	0	[1]	0	[1]
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Current	16	[2]	16	[2]
Noncurrent	0	[2]	0	[2]
Baltimore Gas and Electric Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Current	2		0
Noncurrent	1		0
PECO Energy Co [Member]
Regulatory Liabilities [Line Items]
Current	79		106
Noncurrent	655		629
PECO Energy Co [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
PECO Energy Co [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	479		447
PECO Energy Co [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
PECO Energy Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Current	0		8
Noncurrent	2		0
PECO Energy Co [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Current	0		1
Noncurrent	10		10
PECO Energy Co [Member] | Energy Efficiency Phase [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	32		21
PECO Energy Co [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Current	20		20
Noncurrent	100		114
PECO Energy Co [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Current	8		8
Noncurrent	32		37
PECO Energy Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Current	44	[4]	58	[4]
Noncurrent	0		0
PECO Energy Co [Member] | Over-Recovered Universal Service Fund Costs [Member]
Regulatory Liabilities [Line Items]
Current	4		8
Noncurrent	0		0
PECO Energy Co [Member] | Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Current	0	[1]	0	[1]
Noncurrent	0	[1]	0	[1]
PECO Energy Co [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Current	0	[2]	0	[2]
Noncurrent			0	[2]
PECO Energy Co [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Current	3		3
Noncurrent	0		0
Commonwealth Edison Co [Member]
Regulatory Liabilities [Line Items]
Current	187		170
Noncurrent	3,643		3,512
Commonwealth Edison Co [Member] | Other Postretirement Benefits [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
Commonwealth Edison Co [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	2,371		2,293
Commonwealth Edison Co [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Current	86		78
Noncurrent	1,257		1,219
Commonwealth Edison Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Current	28		45
Noncurrent	0		0
Commonwealth Edison Co [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
Commonwealth Edison Co [Member] | Energy Efficiency Phase [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
Commonwealth Edison Co [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
Commonwealth Edison Co [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
Commonwealth Edison Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Current	26		9
Noncurrent	13		0
Commonwealth Edison Co [Member] | Over-Recovered Universal Service Fund Costs [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	0		0
Commonwealth Edison Co [Member] | Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Current	47	[1]	38	[1]
Noncurrent	0	[1]	0	[1]
Commonwealth Edison Co [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Current	0	[2]	0	[2]
Noncurrent	0	[2]	0	[2]
Commonwealth Edison Co [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Current	0		0
Noncurrent	$ 2		$ 0

[1] Primarily represents the regulatory liability for revenue subject to refund recorded pursuant to the ICC’s order in the 2007 Rate Case. See Note 3 — Regulatory Matters of the Exelon 2013 Form 10-K. for further information.

[2] Represents the electric and gas distribution costs recoverable from customers under BGE’s decoupling mechanism. As of September 30, 2014, BGE had a regulatory asset of $14 million related to under-recovered electric revenue decoupling and a regulatory liability of $16 million related to over-recovered natural gas revenue decoupling. As of December 31, 2013, BGE had a regulatory liability of $7 million related to over-recovered electric revenue decoupling and $9 million related to over-recovered natural gas revenue decoupling.

[3] Relates to $3 million associated with the transmission formula rate and $3 million of over-recovered natural gas supply costs as of September 30, 2014. As of December 31, 2013, includes $1 million of under-recovered electric supply costs and $11 million of over-recovered natural gas supply costs.

[4] Includes $28 million related to the DSP program, $11 million related to the over-recovered natural gas costs under the PGC and $5 million related to over-recovered electric transmission costs as of September 30, 2014. As of December 31, 2013, includes $34 million related to the DSP program, $8 million related to the over-recovered electric transmission costs and $16 million related to the over-recovered natural gas costs under the PGC.