Debt and Credit Agreements - Narrative (Details) $ / shares in Units, shares in Millions				1 Months Ended			12 Months Ended
		Dec. 02, 2015 USD ($)	Sep. 30, 2013 USD ($) MW	Jun. 30, 2014 USD ($) $ / shares shares	Sep. 30, 2012 USD ($) MW	Jul. 31, 2011 USD ($) MW	Dec. 31, 2015 USD ($)		Jan. 05, 2016 USD ($)	Oct. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Sep. 18, 2014 USD ($)	May. 31, 2014 USD ($)	May. 30, 2014 USD ($)	[3],[4]	Mar. 28, 2014 USD ($)	[3],[4]	Feb. 06, 2014 USD ($)	Dec. 31, 2011 USD ($)	Oct. 31, 2011 USD ($)	Jun. 30, 2011 USD ($)
Debt Instrument [Line Items]
Outstanding letters of credit	[1]						$ 1,478,000,000
Bridge loan											$ 3,200,000,000.0				$ 7,200,000,000.0
Long-term debt, gross							25,113,000,000					$ 20,864,000,000
Long-term debt							25,761,000,000
Redemption of debt							44,000,000
Collateral amount of debt							2,400,000,000
Outstanding borrowings/facility draws							0
Debt Instrument, Fee Amount		$ 5,000,000
Payments of Debt Issuance Costs		4,000,000
Write off of Deferred Debt Issuance Cost		9,000,000
Redemption Premium		9,000,000
Designated as Hedging Instrument [Member]
Debt Instrument [Line Items]
Notional amount of preissuance interest rate cash flow hedge derivatives							738,000,000
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross							9,803,000,000					7,071,000,000
Principal amount of debt							3,300,000,000				$ 4,200,000,000
Redemption of debt		868,000,000
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term debt, gross				$ 1,150,000,000.00			$ 1,150,000,000					1,150,000,000
Equity units issued | shares				23
Conversion price | $ / shares				$ 50
Proceeds from issuance of subordinated long-term debt				$ 1,110,000,000
Underwriting fee				35,000,000
Long-term debt				$ 131,000,000
Maximum [Member]
Debt Instrument [Line Items]
Basis points adders for prime-based borrowings							0.065%
Basis points adders for LIBOR-based borrowings							0.00165
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	[2]						$ 8,425,000,000
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	[1]						$ 2,000,000
Basis points adders for prime-based borrowings							0.075%
Basis points adders for LIBOR-based borrowings							0.01075
Long-term debt, gross							$ 6,567,000,000					5,977,000,000
Long-term debt							6,773,000,000
Outstanding borrowings/facility draws							0
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
Exelon Corporate [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	[1]						$ 26,000,000
Basis points adders for prime-based borrowings							0.275%
Basis points adders for LIBOR-based borrowings							0.01275
Long-term debt, gross							$ 5,853,000,000					3,916,000,000
Long-term debt							5,853,000,000
Principal amount of debt		$ 1,900,000,000
Outstanding borrowings/facility draws							0
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] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity							500,000,000	[2]								$ 500,000,000
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	[1]						$ 1,449,000,000
Basis points adders for prime-based borrowings							0.275%
Basis points adders for LIBOR-based borrowings							0.01275
Long-term debt, gross							$ 8,919,000,000					8,134,000,000
Long-term debt							8,919,000,000
Outstanding borrowings/facility draws							0
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] | 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] | 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 | MW					16
Outstanding borrowings/facility draws							32,000,000
Non-recourse debt, hedge percentage					75.00%
Exelon Generation Co L L C [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross							5,971,000,000					5,771,000,000
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]
Line of credit facility, maximum borrowing capacity													$ 131,000,000
Outstanding letters of credit							99,000,000
Interest rate on long-term debt			6.00%
Principal amount of debt			$ 613,000,000
Generation capacity of portfolio | MW			667
Aggregate bank commitments under unsecured revolving credit facilities			$ 10,000,000
Non-recourse debt							572,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | ExGen Texas Power [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt														4.75%
Principal amount of debt														$ 675,000,000
Non-recourse debt							666,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | ExgenRenewablesI425June62021[Member]
Debt Instrument [Line Items]
Interest rate on long-term debt																				4.25%
Long-term debt																				$ 300,000,000
Non-recourse debt							258,000,000
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							69,000,000
Non-recourse debt, commitment																					$ 646,000,000
Non-recourse debt							574,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Sacramento PV Energy [Member]
Debt Instrument [Line Items]
Non-recourse debt, interest rate swap						$ 30,000,000
Generation capacity of portfolio | MW						30
Outstanding borrowings/facility draws							33,000,000
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]
Outstanding borrowings/facility draws																							$ 7,000,000
Non-recourse debt							7,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Holyoke [Member]
Debt Instrument [Line Items]
Outstanding borrowings/facility draws																						$ 11,000,000
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						$ 85,000,000
Non-recourse debt, commitment increase available						$ 500,000,000
Outstanding borrowings/facility draws							68,000,000
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] | Subsequent Event [Member]
Debt Instrument [Line Items]
Outstanding letters of credit									$ 150,000,000
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	[2]						5,725,000,000
PECO Energy Co [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	[1]						$ 1,000,000
Basis points adders for prime-based borrowings							0.00%
Basis points adders for LIBOR-based borrowings							0.009
Long-term debt, gross							$ 2,600,000,000					2,250,000,000
Long-term debt							2,784,000,000
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
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Outstanding letters of credit	[1]						$ 0
Basis points adders for prime-based borrowings							0.00%
Basis points adders for LIBOR-based borrowings							0.01
Long-term debt, gross							$ 1,870,000,000					$ 1,945,000,000
Long-term debt							2,128,000,000
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	[2]						$ 600,000,000

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

[2] Excludes additional credit facilities 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. The agreements for 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 December 31, 2015, letters of credit issued under these facilities totaled $7 million, $14 million, $21 million and $2 million for Generation, ComEd, PECO and BGE, respectively.

[3] Excludes additional credit facilities 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. The agreements for 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 December 31, 2015, letters of credit issued under these facilities totaled $7 million, $14 million, $21 million and $2 million for Generation, ComEd, PECO and BGE, respectively.

[4] Reflects aggregate bank commitments under the revolving and bilateral credit agreements (with the exception of $275 million and $200 million bilateral agreements for Generation as of December 31, 2015 and 2014, respectively) that backstop the commercial paper program. See discussion and Credit Facilities table below for items affecting effective program size.