Debt and Credit Agreements - Commercial Paper Borrowings Outstanding (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 30, 2018	Jun. 30, 2018	Dec. 31, 2017		Dec. 31, 2016	Mar. 31, 2016
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	$ 9,704
Average Interest Rate on Commercial Paper Borrowings		2.15%			1.24%		1.12%
Letters of Credit Outstanding, Amount		$ 1,696
Credit facility agreements with minority and community banks		135			$ 128
Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3],[4]	9,000			9,450
Outstanding commercial paper		89			427
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]
Letters of Credit Outstanding, Amount		9
Exelon Corporate [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	600			600	[4]
Outstanding commercial paper		$ 0			$ 0
Average Interest Rate on Commercial Paper Borrowings		1.93%			1.16%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 200		$ 45
Average Interest Rate on Commercial Paper Borrowings		1.96%			1.23%		1.14%
Credit facility agreements with minority and community banks		$ 49	$ 75		$ 49
Exelon Generation Co L L C [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	5,300			5,300	[4]
Outstanding commercial paper		$ 0			$ 0
Average Interest Rate on Commercial Paper Borrowings		1.96%			1.23%
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount		$ 545			$ 480
Exelon Generation Co L L C [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount		159			$ 179
Exelon Generation Co L L C [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount		$ 5
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		2.14%			1.24%
Letters of Credit Outstanding, Amount		$ 2
Credit facility agreements with minority and community banks		33			$ 34
Commonwealth Edison Co [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	1,000			1,000	[4]
Outstanding commercial paper		$ 0			$ 0
Average Interest Rate on Commercial Paper Borrowings		2.14%			1.24%
PECO Energy Co [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		2.24%			1.13%
Letters of Credit Outstanding, Amount		$ 0
Credit facility agreements with minority and community banks		34			$ 34
PECO Energy Co [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	600			600	[4]
Outstanding commercial paper		$ 0			$ 0
Average Interest Rate on Commercial Paper Borrowings		2.24%			1.13%
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		2.18%			1.28%		0.95%
Letters of Credit Outstanding, Amount		$ 1
Credit facility agreements with minority and community banks		5			$ 5
Baltimore Gas and Electric Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	600			600	[4]
Outstanding commercial paper		$ 35			$ 77
Average Interest Rate on Commercial Paper Borrowings		2.18%			1.28%
Baltimore Gas and Electric Company [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount		$ 2
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 1,500
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		2.24%			1.06%		0.90%
Letters of Credit Outstanding, Amount		$ 8
Credit facility agreements with minority and community banks		5			$ 2
Potomac Electric Power Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	300			500	[4]
Outstanding commercial paper		$ 40			$ 26
Average Interest Rate on Commercial Paper Borrowings		2.24%			1.06%
Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		2.07%			1.48%
Letters of Credit Outstanding, Amount		$ 1
Credit facility agreements with minority and community banks		5			$ 2
Delmarva Power & Light Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	300			500	[4]
Outstanding commercial paper		$ 0			$ 216
Average Interest Rate on Commercial Paper Borrowings		2.07%			1.48%
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		2.21%			1.43%
Letters of Credit Outstanding, Amount		$ 0
Credit facility agreements with minority and community banks		5			$ 2
Atlantic City Electric Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	300			350	[4]
Outstanding commercial paper		$ 14			$ 108
Average Interest Rate on Commercial Paper Borrowings		2.21%			1.43%
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.

[2] At December 31, 2018, 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. At December 31, 2017, excludes $128 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, $34 million, $34 million, $5 million, $2 million, $2 million, and $2 million, respectively.

[3] Excludes $545 million and $480 million in bilateral credit facilities at December 31, 2018 and 2017, respectively, and $159 million and $179 million in credit facilities for project finance at December 31, 2018 and 2017, respectively. These credit facilities do not back Generation's commercial paper program.

[4] 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.