Debt and Credit Agreements - Summary of Bank Commitments, Credit Facility Borrowings and Available Capacity (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Mar. 31, 2016
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	$ 9,704
Facility draws		0
Outstanding letters of credit		1,696
Actual available capacity		8,008
To Support Additional Commercial Paper		7,687
Credit facility agreements with minority and community banks		135			$ 128
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity						$ 500
Exelon Corporate [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit		9
Actual available capacity		591
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		200		$ 45
To Support Additional Commercial Paper		4,097
Credit facility agreements with minority and community banks		49	$ 75		49
Exelon Generation Co L L C [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Outstanding letters of credit		159			179
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Outstanding letters of credit		545			480
Exelon Generation Co L L C [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Outstanding letters of credit		5
Exelon Generation Co L L C [Member] | Line of Credit [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		150
Actual available capacity		192
To Support Additional Commercial Paper		0
Credit facility agreements with minority and community banks		30
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit		2
Actual available capacity		998
To Support Additional Commercial Paper		998
Credit facility agreements with minority and community banks		33			34
PECO Energy Co [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit		0
Actual available capacity		600
To Support Additional Commercial Paper		600
Credit facility agreements with minority and community banks		34			34
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit		1
Actual available capacity		599
To Support Additional Commercial Paper		564
Credit facility agreements with minority and community banks		5			5
Baltimore Gas and Electric Company [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Outstanding letters of credit		2
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit		8
Actual available capacity		292
To Support Additional Commercial Paper		252
Credit facility agreements with minority and community banks		5			2
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		1,500
Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit		1
Actual available capacity		299
To Support Additional Commercial Paper		299
Credit facility agreements with minority and community banks		5			2
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit		0
Actual available capacity		300
To Support Additional Commercial Paper		286
Credit facility agreements with minority and community banks		5			$ 2
Line of Credit [Member] | Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	545
Facility draws		0
Outstanding letters of credit		353
Line of Credit [Member] | Exelon Generation Co L L C [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	159
Facility draws		0
Outstanding letters of credit		119
Actual available capacity		40
To Support Additional Commercial Paper		0
Revolving Credit Facility [Member] | Exelon Corporate [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	600
To Support Additional Commercial Paper		591
Revolving Credit Facility [Member] | Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	5,300
Facility draws		0
Outstanding letters of credit		1,203
Actual available capacity		4,097
Revolving Credit Facility [Member] | Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	1,000
Revolving Credit Facility [Member] | PECO Energy Co [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	600
Revolving Credit Facility [Member] | Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	600
Revolving Credit Facility [Member] | Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	300
Revolving Credit Facility [Member] | Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	300
Revolving Credit Facility [Member] | Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	300
Maximum [Member] | Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		900
Maximum [Member] | Delmarva Power & Light Company [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		0
Maximum [Member] | Atlantic City Electric Company [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 0

[1] Excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $33 million, $34 million, $5 million, $5 million, $5 million and $5 million, respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. As of December 31, 2018, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.