Debt and Credit Agreements - Lines of Credit under Committed Credit Facilities (Details) $ in Millions	Sep. 30, 2015 USD ($)
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 8,500	[1]
Line of Credit Facility, Current Borrowing Capacity	22
Parent [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	500	[1],[2]
Exelon Generation Co L L C [Member] | Community and Minority Banks [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	50
Letters of Credit Outstanding, Amount	7
Exelon Generation Co L L C [Member] | CitiBank [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount	300	[1]
Exelon Generation Co L L C [Member] | CIBC [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount	100	[1]
Exelon Generation Co L L C [Member] | SUMITOMO [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount	100	[1]
Commonwealth Edison Co [Member] | Community and Minority Banks [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	34
Letters of Credit Outstanding, Amount	16
Commonwealth Edison Co [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,000	[1]
PECO Energy Co [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	27
PECO Energy Co [Member] | Community and Minority Banks [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	34
Letters of Credit Outstanding, Amount	21
PECO Energy Co [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	600	[1],[2]
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	27
Baltimore Gas and Electric Company [Member] | Community and Minority Banks [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	5
Letters of Credit Outstanding, Amount	1
Baltimore Gas and Electric Company [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	600	[1],[2]
Syndicated Revolver 1 [Member] | Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	5,100	[1]
Syndicated Revolver 2 [Member] | Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 200	[1]

[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 16, 2015 and were renewed at the same amount through October 14, 2016. These facilities are solely utilized to issue letters of credit. As of September 30, 2015, letters of credit issued under these agreements for Generation, ComEd, PECO and BGE totaled $7 million, $16 million, $21 million and $1 million, respectively.

[2] Syndicated revolvers include credit facility commitments of $22 million, $27 million and $27 million for Exelon Corporate, PECO and BGE, respectively, which expire in August 2018.