Debt and Credit Agreements - Narrative (Details) (USD $)	0 Months Ended	3 Months Ended				0 Months Ended
	Jun. 01, 2014	Mar. 31, 2015		Sep. 30, 2014	Mar. 31, 2014	Jun. 11, 2014	May 01, 2014
Debt Instrument [Line Items]
Repayments of Long-term Debt		$ 580,000,000			$ 1,150,000,000
Line of Credit Facility, Maximum Borrowing Capacity		8,500,000,000	[1]
Bridge Loan		3,200,000,000					7,200,000,000
Interest Expense, Commercial Paper		11,000,000
equity units issued	23,000,000
Investment Banking, Advisory, Brokerage, and Underwriting Fees and Commissions				35,000,000
Subordinated Borrowing, Interest Rate				2.50%
Long-term Debt		131,000,000
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		0			617,000,000
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		18,000,000			532,000,000
Basis points adders for prime-based borrowings		0.275%
Basis Points For Libor Based Borrowings		0.01275
Interest Rate		3.71%
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]
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		1,000,000,000	[1],[2]
Revolving Credit Facility [Member] | PECO Energy Co [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		600,000,000	[1],[2]
Revolving Credit Facility [Member] | Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		600,000,000	[1],[2]
Parent [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		500,000,000	[1],[2]
Convertible Debt Securities [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of Subordinated Long-term Debt				1,110,000,000
Maximum [Member]
Debt Instrument [Line Items]
Basis points adders for prime-based borrowings		0.065%
Basis Points For Libor Based Borrowings		0.00165
SeniorSecuredNotes525January152014Member [Member] | Senior Notes [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt					500,000,000
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						1,150,000,000
SeniorNotesJan152020 [Member] | Senior Notes [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum		2.293%
Interest Rate		2.95%
Debt Instrument, Face Amount		750,000,000
ExgenRenewablesI425June62021[Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount					$ 300,000,000

[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 expire on October 16, 2015. These facilities are solely utilized to issue letters of credit. As of March 31, 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. Also, excludes the unsecured bridge credit facility of $3.2 billion to support the PHI transaction discussed below.

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