Debt and Credit Agreements - Summary of Bank Commitments, Credit Facility Borrowings and Available Capacity (Details) - USD ($)		Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2016	May 26, 2016	Apr. 01, 2016	Jan. 05, 2016	Oct. 23, 2015	Aug. 10, 2013	Aug. 01, 2011
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity				$ 98
Facility draws		$ 0
Outstanding letters of credit	[1]	1,147,000,000
Actual available capacity		8,333,000,000
To Support Additional Commercial Paper	[2]	7,657,000,000
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity									$ 500,000,000
Exelon Corporate [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	45,000,000
Actual available capacity		555,000,000
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		200,000,000
To Support Additional Commercial Paper		4,432,000,000
Credit facility agreements with minority and community banks		49,000,000
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Outstanding letters of credit		480,000,000	$ 500,000,000
Exelon Generation Co L L C [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Outstanding letters of credit		5,000,000
Exelon Generation Co L L C [Member] | Line of Credit [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity						$ 200,000,000	$ 150,000,000	$ 100,000,000
Actual available capacity		249,000,000
To Support Additional Commercial Paper	[2]	0
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	2,000,000
Actual available capacity		998,000,000
To Support Additional Commercial Paper	[2]	998,000,000
Credit facility agreements with minority and community banks		34,000,000
PECO Energy Co [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	1,000,000
Actual available capacity		599,000,000
To Support Additional Commercial Paper	[2]	599,000,000
Credit facility agreements with minority and community banks		34,000,000
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	0
Actual available capacity		600,000,000
To Support Additional Commercial Paper	[2]	523,000,000
Credit facility agreements with minority and community banks		5,000,000
Baltimore Gas and Electric Company [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Outstanding letters of credit		2,000,000
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity					$ 900,000,000					$ 1,500,000,000
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	0
Actual available capacity		300,000,000
To Support Additional Commercial Paper	[2]	274,000,000
Delmarva Power and Light Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	0
Actual available capacity		300,000,000
To Support Additional Commercial Paper	[2]	84,000,000
Credit facility agreements with minority and community banks		2,000,000
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	0
Actual available capacity		300,000,000
To Support Additional Commercial Paper	[2]	192,000,000
Credit facility agreements with minority and community banks		2,000,000
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	9,480,000,000
Revolving Credit Facility [Member] | Exelon Corporate [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	600,000,000
To Support Additional Commercial Paper	[2]	555,000,000
Revolving Credit Facility [Member] | Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		5,300,000,000
Facility draws		0
Outstanding letters of credit		868,000,000
Actual available capacity		4,432,000,000
Revolving Credit Facility [Member] | Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	1,000,000,000
Revolving Credit Facility [Member] | PECO Energy Co [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	600,000,000
Revolving Credit Facility [Member] | Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	600,000,000
Revolving Credit Facility [Member] | Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	300,000,000
Revolving Credit Facility [Member] | Delmarva Power and Light Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	300,000,000
Revolving Credit Facility [Member] | Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	$ 300,000,000

[1] Excludes nonrecourse debt letters of credit, see discussion below on Antelope Valley Solar Ranch One and Continental Win

[2] Pepco, DPL and ACE's revolving credit facility is subject to available borrowing capacity. The borrowing capacity may be increased or decreased during the term of the facility, except that (i) the sum of the borrowing capacity must equal the total amount of the facility, and (ii) the aggregate amount of credit used at any given time by each of Pepco, DPL or ACE may not exceed $900 million or the maximum amount of short-term debt the company is permitted to have outstanding by its regulatory authorities. The total number of the borrowing reallocations may not exceed eight per year during the term of the facility.

[3] Excludes additional credit facility agreements for Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $34 million, $34 million, $5 million, $2 million, $2 million and $2 million, respectively, arranged with minority and community banks located primarily within utilities' service territories. These facilities expire on October 12, 2018. These facilities are solely utilized to issue letters of credit. As of December 31, 2017, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.