Debt and Credit Agreements - Narrative (Details) $ / shares in Units, shares in Millions		12 Months Ended
		Dec. 31, 2018 USD ($) MW		Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) $ / shares	Dec. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2016 USD ($)	Oct. 23, 2015 USD ($)	Jun. 30, 2014 USD ($) $ / shares shares
Debt Instrument [Line Items]
2019		$ 1,349,000,000
Long-term Debt, Current Maturities		1,349,000,000	[1]	$ 2,088,000,000
Repayments of Long-term Debt		1,786,000,000		2,490,000,000	$ 1,936,000,000
Line of credit facility, maximum borrowing capacity	[2]	9,704,000,000
Outstanding letters of credit		1,696,000,000
Long-term debt, gross		34,911,000,000		33,657,000,000
Long-term debt		35,301,000,000
Collateral amount of debt		3,000,000,000
Outstanding borrowings/facility draws		0
Line of Credit Facility, Current Borrowing Capacity		$ 135,000,000		128,000,000
Credit agreement threshold		2.50
Transition Bonds [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 59,000,000		90,000,000
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross		11,285,000,000		11,285,000,000
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,150,000,000		$ 1,150,000,000
Equity units issued | shares										23
Conversion price | $ / shares										$ 50
Interest rate on long-term debt				3.497%						2.50%
Stock Issued During Period, Shares, Treasury Stock Reissued | shares				33
Junior Subordinated Notes				$ 1,150,000,000						$ 1,150,000,000
Loss on Reissuance, Treasury Stock				1,050,000,000
Maximum [Member]
Debt Instrument [Line Items]
Basis points adders for prime-based borrowings		90.00%
Basis points adders for LIBOR-based borrowings		1.7
Maximum [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		5.55%
Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		7.60%
Maximum [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		3.50%
Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		2.45%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity								$ 500,000,000
Exelon Corporate [Member]
Debt Instrument [Line Items]
2019		$ 0
Repayments of Long-term Debt		0		569,000,000	46,000,000
Outstanding letters of credit		9,000,000
Long-term debt, gross		7,039,000,000		7,039,000,000
Long-term debt		7,039,000,000
Outstanding borrowings/facility draws		0
Exelon Corporate [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross	[3]	5,889,000,000		5,889,000,000
Exelon Corporate [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,150,000,000		1,150,000,000
Exelon Corporate [Member] | Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[3]	7.60%
Exelon Corporate [Member] | Maximum [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		3.50%
Exelon Corporate [Member] | Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[3]	2.45%
Exelon Corporate [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	[2]	$ 600,000,000
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
2019		906,000,000
Long-term Debt, Current Maturities		906,000,000		346,000,000
Repayments of Long-term Debt		141,000,000		1,261,000,000	202,000,000
Line of credit facility, maximum borrowing capacity		200,000,000					$ 45,000,000
Long-term debt, gross		8,759,000,000		8,955,000,000
Long-term debt		8,759,000,000
Line of Credit Facility, Current Borrowing Capacity		$ 49,000,000		49,000,000		$ 75,000,000
Credit agreement threshold		3.00
Exelon Generation Co L L C [Member] | ExGen Texas Power [Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		2.34%
Non-recourse debt, interest rate swap		$ 505,000,000
Exelon Generation Co L L C [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross		6,019,000,000		6,019,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt					31,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | ExGen Texas Power [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		675,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | DOE Project Financing, 3.092% January 2, 2037 [Member]
Debt Instrument [Line Items]
Outstanding letters of credit		38,000,000
Non-recourse debt, commitment		$ 646,000,000
Debt, Weighted Average Interest Rate		2.82%
Non-recourse debt		$ 508,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Denver International Airport [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		5.50%
Outstanding borrowings/facility draws		$ 7,000,000
Non-recourse debt		$ 6,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Holyoke [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		5.25%
Outstanding borrowings/facility draws		$ 11,000,000
Non-recourse debt		8,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Upstream Gas Property [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt					15,000,000
Escrow Deposit					6,000,000
Gain (Loss) on Sale of Debt Investments					37,000,000
Long-term debt		$ 15,000,000		15,000,000
Outstanding borrowings/facility draws					22,000,000
Proceeds from Sales of Business, Affiliate and Productive Assets				1,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | SolGen [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		3.93%
Debt Instrument, Face Amount		$ 150,000,000
Non-recourse debt		$ 137,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Renewable Power Generation [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		4.11%
Debt Instrument, Face Amount		$ 150,000,000
Non-recourse debt		115,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Continetal Wind [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		131,000,000
Aggregate Bank Commitments Under Unsecured Revolving Credit Facilities		10,000,000
Outstanding letters of credit		$ 114,000,000
Interest rate on long-term debt		6.00%
Debt Instrument, Face Amount		$ 613,000,000
Generation capacity of portfolio | MW		667
Non-recourse debt		$ 479,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | ExGenRenewablesIVNov2024 [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		3.00%
Long-term debt		$ 850,000,000
Non-recourse debt, interest rate swap		636,000,000
Non-recourse debt		$ 834,000,000
Non-recourse debt, hedge percentage		2.32%
Proceeds from Issuance of Debt		$ 785,000,000
Proceeds from (Repayments of) Restricted Cash, Financing Activities		$ 50,000,000
Exelon Generation Co L L C [Member] | Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		7.60%
Exelon Generation Co L L C [Member] | Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		2.95%
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	[2]	$ 5,300,000,000
Outstanding letters of credit		1,203,000,000
Outstanding borrowings/facility draws		0
Exelon Generation Co L L C [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	[2]	545,000,000
Outstanding letters of credit		353,000,000
Outstanding borrowings/facility draws		0
Exelon Generation Co L L C [Member] | Domestic Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		95,000,000				$ 100,000,000
Exelon Generation Co L L C [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		150,000,000
Line of Credit Facility, Current Borrowing Capacity		30,000,000
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Outstanding letters of credit		545,000,000		480,000,000
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
2019		300,000,000
Long-term Debt, Current Maturities		300,000,000	[4]	840,000,000
Repayments of Long-term Debt		840,000,000		425,000,000	665,000,000
Outstanding letters of credit		2,000,000
Long-term debt, gross		8,187,000,000		7,676,000,000
Long-term debt		8,393,000,000
Outstanding borrowings/facility draws		0
Line of Credit Facility, Current Borrowing Capacity		$ 33,000,000		34,000,000
Credit agreement threshold		2.00
Commonwealth Edison Co [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	[2]	$ 1,000,000,000
PECO Energy Co [Member]
Debt Instrument [Line Items]
2019		0
Repayments of Long-term Debt		500,000,000		0	300,000,000
Outstanding letters of credit		0
Long-term debt, gross		3,125,000,000		2,925,000,000
Long-term debt		3,309,000,000
Outstanding borrowings/facility draws		0
Line of Credit Facility, Current Borrowing Capacity		$ 34,000,000		34,000,000
Credit agreement threshold		2.00
PECO Energy Co [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	[2]	$ 600,000,000
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
2019		0
Repayments of Long-term Debt		0		41,000,000	$ 379,000,000
Outstanding letters of credit		1,000,000
Long-term debt, gross		2,900,000,000		2,600,000,000
Long-term debt		2,900,000,000
Outstanding borrowings/facility draws		0
Line of Credit Facility, Current Borrowing Capacity		$ 5,000,000		5,000,000
Preferred Stock, Redemption Price Per Share | $ / shares					$ 100
Credit agreement threshold		2.00
Baltimore Gas and Electric Company [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 2,900,000,000		2,600,000,000
Baltimore Gas and Electric Company [Member] | Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		6.35%
Baltimore Gas and Electric Company [Member] | Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		2.40%
Baltimore Gas and Electric Company [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	[2]	$ 600,000,000
Pepco Holdings LLC [Member]
Debt Instrument [Line Items]
2019		125,000,000
Repayments of Long-term Debt		299,000,000		169,000,000
Long-term debt, gross		5,636,000,000		5,189,000,000
Long-term debt		5,636,000,000
Short-term Bank Loans and Notes Payable		$ 500,000,000
Debt Instrument, Interest Rate Terms		LIBOR plus 1%
Pepco Holdings LLC [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Long-term debt, gross	[5]	$ 59,000,000		90,000,000
Pepco Holdings LLC [Member] | Maximum [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[5]	5.55%
Pepco Holdings LLC [Member] | Minimum [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[5]
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 1,500,000,000
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		900,000,000
Potomac Electric Power Company [Member]
Debt Instrument [Line Items]
2019		15,000,000
Repayments of Long-term Debt		14,000,000		13,000,000	$ 11,000,000
Outstanding letters of credit		8,000,000
Long-term debt, gross		2,751,000,000		2,570,000,000
Long-term debt		2,751,000,000
Outstanding borrowings/facility draws		0
Line of Credit Facility, Current Borrowing Capacity		$ 5,000,000		2,000,000
Credit agreement threshold		2.00
Potomac Electric Power Company [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	[2]	$ 300,000,000
Delmarva Power & Light Company [Member]
Debt Instrument [Line Items]
2019		91,000,000
Long-term Debt, Current Maturities		79,000,000		79,000,000
Repayments of Long-term Debt		4,000,000		40,000,000	100,000,000
Outstanding letters of credit		1,000,000
Long-term debt, gross		1,504,000,000		1,309,000,000
Long-term debt		1,504,000,000
Outstanding borrowings/facility draws		0
Line of Credit Facility, Current Borrowing Capacity		$ 5,000,000		2,000,000
Credit agreement threshold		2.00
Delmarva Power & Light Company [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	[2]	$ 300,000,000
Delmarva Power & Light Company [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		0
Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
2019		18,000,000
Repayments of Long-term Debt		281,000,000		35,000,000	$ 48,000,000
Outstanding letters of credit		0
Long-term debt, gross		1,196,000,000		1,127,000,000
Long-term debt		1,196,000,000
Outstanding borrowings/facility draws		0
Short-term Bank Loans and Notes Payable		$ 125,000,000
Debt Instrument, Interest Rate Terms		LIBOR plus 0.55%
Line of Credit Facility, Current Borrowing Capacity		$ 5,000,000		2,000,000
Credit agreement threshold		2.00
Atlantic City Electric Company [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
2019		$ 18,000,000
Long-term debt, gross	[6]	$ 59,000,000		$ 90,000,000
Atlantic City Electric Company [Member] | Maximum [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[6]	5.55%
Atlantic City Electric Company [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	[2]	$ 300,000,000
Atlantic City Electric Company [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		0
Corporate, Non-Segment [Member] | Exelon Corporate [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable		$ 500,000,000
Debt Instrument, Interest Rate Terms		LIBOR plus 1%
CENG [Member] | Exelon Generation Co L L C [Member] | Domestic Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 200,000,000
CENG [Member] | Exelon Generation Co L L C [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity									$ 100,000,000

[1] In January 2019, $300 million of ComEd long-term debt due within one year was paid in full.

[2] 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.

[3] Senior unsecured notes include mirror debt that is held on both Generation and Exelon Corporation's balance sheets.

[4] In January 2019, the $300 million balance was paid in full.

[5] Transition bonds are recorded as part of Long-term debt within ACE's Consolidated Balance Sheets.

[6] Maturities of ACE's Transition Bonds outstanding at December 31, 2018 are $18 million in 2019, $20 million in 2020 and $21 million in 2021.