Debt and Credit Agreements - Commercial Paper Borrowings Outstanding (Details) - USD ($)		Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity				$ 98
Letters of Credit Outstanding, Amount	[1]	$ 1,147,000,000
Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	9,450,000,000	$ 9,450,000,000
Outstanding commercial paper		$ 427,000,000	$ 688,000,000
Exelon Corporate [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		1.24%	1.12%		0.88%
Letters of Credit Outstanding, Amount	[1]	$ 45,000,000
Exelon Corporate [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	600,000,000	$ 600,000,000
Outstanding commercial paper		$ 0	$ 0
Average Interest Rate on Commercial Paper Borrowings		1.16%	0.70%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 200,000,000
Average Interest Rate on Commercial Paper Borrowings		1.23%	1.14%
Line of Credit Facility, Current Borrowing Capacity		$ 49,000,000
Exelon Generation Co L L C [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	5,300,000,000	$ 5,300,000,000
Outstanding commercial paper		$ 0	$ 620,000,000
Average Interest Rate on Commercial Paper Borrowings		1.23%	0.94%
Exelon Generation Co L L C [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount		$ 5,000,000
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		1.24%			0.89%
Letters of Credit Outstanding, Amount	[1]	$ 2,000,000
Line of Credit Facility, Current Borrowing Capacity		34,000,000
Commonwealth Edison Co [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	1,000,000,000	$ 1,000,000,000
Outstanding commercial paper		$ 0	$ 0
Average Interest Rate on Commercial Paper Borrowings		1.24%	0.77%
PECO Energy Co [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		1.13%
Letters of Credit Outstanding, Amount	[1]	$ 1,000,000
Line of Credit Facility, Current Borrowing Capacity		34,000,000
PECO Energy Co [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	600,000,000	$ 600,000,000
Outstanding commercial paper		$ 0	$ 0
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		1.28%	0.95%		0.87%
Letters of Credit Outstanding, Amount	[1]	$ 0
Line of Credit Facility, Current Borrowing Capacity		5,000,000
Baltimore Gas and Electric Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	600,000,000	$ 600,000,000
Outstanding commercial paper		$ 77,000,000	$ 45,000,000
Average Interest Rate on Commercial Paper Borrowings		1.28%	0.77%
Baltimore Gas and Electric Company [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount		$ 2,000,000
Pepco Energy Services [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Current Borrowing Capacity		$ 2,000,000
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings					1.22%
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		1.06%	0.90%		0.68%
Letters of Credit Outstanding, Amount	[1]	$ 0
Potomac Electric Power Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	500,000,000	$ 500,000,000
Outstanding commercial paper		$ 26,000,000	$ 23,000,000
Average Interest Rate on Commercial Paper Borrowings		1.06%	0.71%
Delmarva Power and Light Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		1.48%			0.79%
Letters of Credit Outstanding, Amount	[1]	$ 0
Line of Credit Facility, Current Borrowing Capacity		2,000,000
Delmarva Power and Light Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	500,000,000	$ 500,000,000
Outstanding commercial paper		$ 216,000,000	$ 0
Average Interest Rate on Commercial Paper Borrowings		1.48%	0.68%
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		1.43%			0.65%
Letters of Credit Outstanding, Amount	[1]	$ 0
Line of Credit Facility, Current Borrowing Capacity		2,000,000
Atlantic City Electric Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	350,000,000	$ 350,000,000
Outstanding commercial paper		$ 108,000,000	$ 0
Average Interest Rate on Commercial Paper Borrowings		1.43%	0.65%

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

[2] Excludes $480 million and $500 million in bilateral credit facilities that do not back Generation's commercial paper program at December 31, 2017 and 2016, respectively

[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.