Debt and Credit Agreements - Narrative (Details) $ in Millions				9 Months Ended
		Oct. 05, 2015 USD ($)	Jun. 11, 2014 USD ($) shares	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Oct. 23, 2015 USD ($)	May. 01, 2014 USD ($)
Debt Instrument [Line Items]
Repayments of Long-term Debt				$ 1,745	$ 1,214
equity units issued | shares			23,000,000
Investment Banking, Advisory, Brokerage, and Underwriting Fees and Commissions			$ 35
Subordinated Borrowing, Interest Rate			2.50%
Long-term Debt			$ 131
Line of Credit Facility, Maximum Borrowing Capacity	[1]			$ 8,500
Parent Company [Member]
Debt Instrument [Line Items]
Basis points adders for prime-based borrowings				0.275%
Basis Points For Libor Based Borrowings				0.01275
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt				$ 260	617
Basis points adders for prime-based borrowings				0.075%
Basis Points For Libor Based Borrowings				0.01075
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt				$ 64	552
Basis points adders for prime-based borrowings				0.275%
Basis Points For Libor Based Borrowings				0.01275
PECO Energy Co [Member]
Debt Instrument [Line Items]
Basis points adders for prime-based borrowings				0.00%
Basis Points For Libor Based Borrowings				0.009
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt				$ 37	35
Basis points adders for prime-based borrowings				0.00%
Basis Points For Libor Based Borrowings				0.01
Revolving Credit Facility [Member] | Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	[1]			$ 1,000
Revolving Credit Facility [Member] | PECO Energy Co [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	[1],[2]			600
Revolving Credit Facility [Member] | Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	[1],[2]			600
Parent [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	[1],[2]			$ 500
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage				1.00%
Unamortized Debt Issuance Expense				$ 22
Senior Notes [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt					$ 9
Interest Rate					4.40%
Debt Instrument, Face Amount	[3]			750
Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount							$ 4,200
Convertible Debt Securities [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of Subordinated Long-term Debt			1,110
Junior Subordinated Debt [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt				$ 33
ExGen425Feb062021 [Member] | Senior Notes [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount					$ 300
AGE143Nov172017 [Member] | Senior Notes [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Interest Rate				1.43%
Debt Instrument, Face Amount				$ 74
TaxExemptBonds255 [Member] | First Mortgage Bonds [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	[4]			$ 435
TaxExemptBonds255 [Member] | Maximum [Member] | First Mortgage Bonds [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Interest Rate				2.70%
TaxExemptBonds255 [Member] | Minimum [Member] | First Mortgage Bonds [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Interest Rate				2.50%
AVSR [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt				$ 12
Debt Instrument, Face Amount				$ 39	$ 125
AVSR [Member] | Maximum [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Interest Rate				2.96%	3.14%
AVSR [Member] | Minimum [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Interest Rate				2.29%	3.06%
SeniorSecuredNotes525January152014Member [Member] | Senior Notes [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt					$ 500
Interest Rate					5.35%
SeniorSecuredNotes525January152014Member [Member] | Junior Subordinated Debt [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt			$ 1,150
Subsequent Event [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity						$ 100
Subsequent Event [Member] | First Mortgage Bonds [Member] | PECO Energy Co [Member]
Debt Instrument [Line Items]
Long-term Debt		$ 350
Interest Rate		3.15%
Subsequent Event [Member] | AVSR [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Repayments of Secured Debt		$ 10
Bridge Loan [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity							3,200
Line of Credit Facility, Maximum Borrowing Capacity							$ 7,200

[1] Excludes additional credit facility agreements for Generation, ComEd, PECO and BGE with aggregate commitments of $50 million, $34 million, $34 million and $5 million, respectively, arranged with minority and community banks located primarily within ComEd’s, PECO’s and BGE’s service territories. These facilities expired on October 16, 2015 and were renewed at the same amount through October 14, 2016. These facilities are solely utilized to issue letters of credit. As of September 30, 2015, letters of credit issued under these agreements for Generation, ComEd, PECO and BGE totaled $7 million, $16 million, $21 million and $1 million, respectively.

[2] Syndicated revolvers include credit facility commitments of $22 million, $27 million and $27 million for Exelon Corporate, PECO and BGE, respectively, which expire in August 2018.

[3] In connection with the issuance of Senior Unsecured Notes, Exelon terminated floating-to-fixed interest rate swaps that had been designated as cash flow hedges. See Note 10 — Derivative Financial Instruments for further information on the swap termination.

[4] The Tax Exempt Pollution Control Revenue Bonds have a mandatory put date that ranges from March 1, 2019 - September 1, 2020.