Debt and Credit Agreements - Commercial Paper Borrowings Outstanding (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013		May 30, 2014		Mar. 28, 2014
Commercial Paper [Member]
Short-term Debt [Line Items]
Maximum Program Size	$ 8,300,000,000	[1],[2]	$ 8,300,000,000	[1],[2]
Outstanding commercial paper	424,000,000		319,000,000
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum Program Size	8,500,000,000	[3]
Exelon Corporate [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings	0.53%		0.35%
Exelon Corporate [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Maximum Program Size			500,000,000	[1],[2]
Outstanding commercial paper	0		0
Average Interest Rate on Commercial Paper Borrowings	0.00%		0.27%
Exelon Corporate [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum Program Size	500,000,000	[3]			500,000,000	[1],[2]
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Bilateral letters of credit	200,000,000
Exelon Generation Co L L C [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Maximum Program Size	5,600,000,000	[1],[2]	5,600,000,000	[1],[2]
Outstanding commercial paper	0		0
Average Interest Rate on Commercial Paper Borrowings	0.32%		0.32%
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum Program Size	5,800,000,000	[3]			5,300,000,000.0	[2]
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings	0.50%		0.37%
Commonwealth Edison Co [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Maximum Program Size			1,000,000,000	[1],[2]
Outstanding commercial paper	304,000,000		184,000,000
Average Interest Rate on Commercial Paper Borrowings	0.33%		0.40%
Commonwealth Edison Co [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum Program Size	1,000,000,000	[3]					1,000,000,000	[1],[2]
PECO Energy Co [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Maximum Program Size			600,000,000	[1],[2]
Outstanding commercial paper	0		0
PECO Energy Co [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum Program Size	600,000,000	[3]			600,000,000	[1],[2]
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings	0.61%		0.31%
Baltimore Gas and Electric Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Maximum Program Size			600,000,000	[1],[2]	600,000,000	[1],[2]
Outstanding commercial paper	120,000,000		135,000,000
Average Interest Rate on Commercial Paper Borrowings	0.29%		0.31%
Baltimore Gas and Electric Company [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum Program Size	$ 600,000,000	[3]

[1] Excludes additional credit facility agreements for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million, $34 million, $34 million and $5 million, respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. These facilities expired on October 17, 2014 and were renewed at the same amount through October 16, 2015. These facilities are solely utilized to issue letters of credit. As of December 31, 2014, letters of credit issued under these agreements totaled $9 million, $16 million, $21 million and $1 million for Generation, ComEd, PECO and BGE, respectively. Also, excludes the unsecured bridge credit facility of $3.2 billion at December 31, 2014, to support the PHI transaction discussed below.

[2] aggregate bank commitments under the revolving and bilateral credit agreements (with the exception of $200 million bilateral agreements for Generation) that backstop the commercial paper program. See discussion below and Credit Agreements table below for items affecting effective program size.

[3] Excludes additional credit facility agreements for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million, $34 million, $34 million and $5 million, respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. These facilities expired on October 17, 2014 and were renewed at the same amount through October 16, 2015. These facilities are solely utilized to issue letters of credit. As of December 31, 2014, letters of credit issued under these agreements totaled $9 million, $16 million, $21 million and $1 million for Generation, ComEd, PECO and BGE, respectively. Also, excludes the unsecured bridge credit facility of $3.2 billion at December 31, 2014, to support the PHI transaction discussed below