Debt and Credit Agreements - Narrative (Details) (USD $)	1 Months Ended	3 Months Ended	0 Months Ended	12 Months Ended		0 Months Ended	1 Months Ended
	Jun. 30, 2014	Jun. 30, 2014	Sep. 30, 2013 MW	Dec. 31, 2014		Jan. 13, 2015	Jul. 31, 2011 MW	Sep. 30, 2012 MW	Jun. 11, 2014	May 31, 2014	Dec. 31, 2013	May 30, 2014		Mar. 28, 2014		Sep. 18, 2014	Feb. 06, 2014	Oct. 24, 2014
Debt Instrument [Line Items]
Outstanding letters of credit				$ 1,190,000,000	[1]
Bridge loan									3,200,000,000.0	7,200,000,000.0
Long-term debt, gross				20,756,000,000							18,760,000,000
Equity units issued	23,000,000
Underwriting fee	60,000,000	35,000,000
Equity units, annual distribution rate	6.50%
Forward contract, payment rate	4.00%
Long-term debt	131,000,000	131,000,000		21,404,000,000
Collateral amount of debt				2,700,000,000
Outstanding borrowings/facility draws				0
Debt Continental Project [Member]
Debt Instrument [Line Items]
Generation capacity of portfolio			667
Designated as Hedging Instrument [Member]
Debt Instrument [Line Items]
Notional amount of preissuance interest rate cash flow hedge derivatives				3,070,000,000
Long Term Debt Issuances [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	2.50%	2.50%
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross				7,071,000,000							7,571,000,000
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term debt, gross	1,150,000,000.00	1,150,000,000.00		1,150,000,000							0
Convertible Debt Securities [Member]
Debt Instrument [Line Items]
Conversion price	$ 50	$ 50
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 adders for LIBOR-based borrowings				0.00165
Equity units, share price	$ 43.7484
Common shares, issuable at maturity	1.1429
Minimum [Member]
Debt Instrument [Line Items]
Equity units, share price	$ 35
Common shares, issuable at maturity	1.4286
Revolving Credit Facility [Member] | Parent [Member]
Debt Instrument [Line Items]
Line of credit facility, cumulative committed amount												315,000,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				8,500,000,000	[2]
Bridge Loan [Member]
Debt Instrument [Line Items]
Interest expense, short-term borrowings				31,000,000
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Additional amounts available upon request under current credit facilities														500,000,000
Outstanding letters of credit				2,000,000	[1]
Basis points adders for prime-based borrowings				0.075%
Basis points adders for LIBOR-based borrowings				0.01075
Long-term debt, gross				5,977,000,000							5,694,000,000
Interest rate on long-term debt				6.35%	[3]
Long-term debt				6,183,000,000
Outstanding borrowings/facility draws				0
Commonwealth Edison Co [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity														500,000,000	[4]
Commonwealth Edison Co [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				1,000,000,000	[2]									1,000,000,000	[4],[5]
Exelon Corporate [Member]
Debt Instrument [Line Items]
Outstanding letters of credit				6,000,000	[1]
Basis points adders for prime-based borrowings				0.275%
Basis points adders for LIBOR-based borrowings				0.01275
Long-term debt, gross				3,808,000,000							2,658,000,000
Long-term debt				3,808,000,000
Outstanding borrowings/facility draws				0
Exelon Corporate [Member] | Senior Notes [Member] | Subsequent Event [Member] | Fixed Rate Note, 4.55% Due 2015 [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt						4.55%
Redemption of debt						550,000,000
Exelon Corporate [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term debt, gross				1,150,000,000							0
Exelon Corporate [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				500,000,000	[2]							500,000,000	[4],[5]
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Outstanding letters of credit				1,181,000,000	[1]
Basis points adders for prime-based borrowings				0.275%
Basis points adders for LIBOR-based borrowings				0.01275
Long-term debt, gross				8,134,000,000							7,552,000,000
Long-term debt				8,134,000,000
Outstanding borrowings/facility draws				0
Exelon Generation Co L L C [Member] | Debt Continental Project [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt			6.00%
Principal amount of debt			613,000,000
Exelon Generation Co L L C [Member] | Continetal Wind [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			131,000,000
Outstanding letters of credit				47,000,000
Aggregate bank commitments under unsecured revolving credit facilities			10,000,000
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Debt Instrument [Line Items]
Notional amount of preissuance interest rate cash flow hedge derivatives				770,000,000
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Debt Continental Project [Member]
Debt Instrument [Line Items]
Non-recourse debt, interest rate swap			350,000,000
Gain from exchange offer			26,000,000
Exelon Generation Co L L C [Member] | ExGen Texas Power [Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Non-recourse debt, interest rate swap																505,000,000
Exelon Generation Co L L C [Member] | ExgenRenewablesI425June62021[Member] | Interest Rate Swap [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt																	2.03%
Non-recourse debt, interest rate swap																	240,000,000
Exelon Generation Co L L C [Member] | Sacramento PV Energy [Member]
Debt Instrument [Line Items]
Non-recourse debt, interest rate swap							30,000,000
Generation capacity of portfolio							30
Outstanding borrowings/facility draws				35,000,000
Exelon Generation Co L L C [Member] | Constellation Solar Horizons Financing [Member]
Debt Instrument [Line Items]
Non-recourse debt, interest rate swap								29,000,000
Non-recourse debt, commitment								38,000,000
Generation capacity of portfolio								16
Outstanding borrowings/facility draws				34,000,000
Non-recourse debt, hedge percentage								75.00%
Exelon Generation Co L L C [Member] | Denver International Airport [Member]
Debt Instrument [Line Items]
Outstanding borrowings/facility draws				7,000,000
Exelon Generation Co L L C [Member] | Holyoke [Member]
Debt Instrument [Line Items]
Outstanding borrowings/facility draws				10,000,000
Exelon Generation Co L L C [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross				5,771,000,000							6,271,000,000
Exelon Generation Co L L C [Member] | Senior Notes [Member] | ExGen Texas Power [Member]
Debt Instrument [Line Items]
Principal amount of debt																675,000,000
Exelon Generation Co L L C [Member] | Senior Notes [Member] | ExGen Texas Power [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt																4.75%
Exelon Generation Co L L C [Member] | Senior Notes [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt						2.95%
Principal amount of debt						750,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Continetal Wind [Member]
Debt Instrument [Line Items]
Non-recourse debt				592,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | ExGen Texas Power [Member]
Debt Instrument [Line Items]
Non-recourse debt				673,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | ExgenRenewablesI425June62021[Member]
Debt Instrument [Line Items]
Non-recourse debt				282,000,000
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				156,000,000
Non-recourse debt				557,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Sacramento PV Energy [Member]
Debt Instrument [Line Items]
Non-recourse debt							41,000,000
Non-recourse debt, hedge percentage							75.00%
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Denver International Airport [Member]
Debt Instrument [Line Items]
Non-recourse debt				7,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Holyoke [Member]
Debt Instrument [Line Items]
Non-recourse debt				10,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Upstream Gas Property [Member]
Debt Instrument [Line Items]
Non-recourse debt, commitment				110,000,000
Non-recourse debt, commitment increase available				500,000,000
Outstanding borrowings/facility draws				77,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Long Term Debt Issuances [Member] | ExGen Texas Power [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt																2.34%
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Long Term Debt Issuances [Member] | ExgenRenewablesI425June62021[Member]
Debt Instrument [Line Items]
Interest rate on long-term debt																	4.25%
Long-term debt																	300,000,000
Exelon Generation Co L L C [Member] | DOE Financing Project [Member] | DOE Project Financing, 3.092% January 2, 2037 [Member]
Debt Instrument [Line Items]
Non-recourse debt, interest rate swap				485,000,000
Non-recourse debt, commitment				646,000,000
Exelon Generation Co L L C [Member] | Sumitomo Bank [Member]
Debt Instrument [Line Items]
Outstanding letters of credit																		100,000,000
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				5,800,000,000	[2]							5,300,000,000.0	[4]
PECO Energy Co [Member]
Debt Instrument [Line Items]
Outstanding letters of credit				1,000,000	[1]
Basis points adders for prime-based borrowings				0.00%
Basis points adders for LIBOR-based borrowings				0.009
Long-term debt, gross				2,250,000,000							2,200,000,000
Long-term debt				2,434,000,000
Outstanding borrowings/facility draws				0
PECO Energy Co [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				600,000,000	[2]							600,000,000	[4],[5]
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Outstanding letters of credit				0	[1]
Basis points adders for prime-based borrowings				0.00%
Basis points adders for LIBOR-based borrowings				0.01
Long-term debt, gross				1,945,000,000							2,015,000,000
Long-term debt				2,203,000,000
Outstanding borrowings/facility draws				0
Baltimore Gas and Electric Company [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				600,000,000	[2]
Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Debt Instrument [Line Items]
Notional amount of preissuance interest rate cash flow hedge derivatives				400,000,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member]
Debt Instrument [Line Items]
Notional amount of preissuance interest rate cash flow hedge derivatives				$ 26,000,000

[1] Excludes nonrecourse debt letters of credit, see discussion below on Continental Wind.

[2] 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 17, 2014 and were renewed at the same amount through October 16, 2015. These facilities are solely utilized to issue letters of credit. As of December 31, 2014, letters of credit issued under these agreements totaled $9 million, $16 million, $21 million and $1 million for Generation, ComEd, PECO and BGE, respectively. Also, excludes the unsecured bridge credit facility of $3.2 billion at December 31, 2014, to support the PHI transaction discussed below

[3] Amount owed to this financing trust is recorded as Long-term debt to financing trust within ComEd’s Consolidated Balance Sheets.

[4] aggregate bank commitments under the revolving and bilateral credit agreements (with the exception of $200 million bilateral agreements for Generation) that backstop the commercial paper program. See discussion below and Credit Agreements table below for items affecting effective program size.

[5] 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 17, 2014 and were renewed at the same amount through October 16, 2015. These facilities are solely utilized to issue letters of credit. As of December 31, 2014, letters of credit issued under these agreements totaled $9 million, $16 million, $21 million and $1 million for Generation, ComEd, PECO and BGE, respectively. Also, excludes the unsecured bridge credit facility of $3.2 billion at December 31, 2014, to support the PHI transaction discussed below.