Debt and Credit Agreements - Summary of Outstanding Long-term Debt (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Jun. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 20,756,000,000			$ 18,760,000,000
Unamortized debt discount and premium, net	(37,000,000)			(19,000,000)
Long-term debt (including amounts due within one year)	441,000,000			384,000,000
Fair value hedge carrying value adjustment, net	4,000,000			7,000,000
Long-term debt due within one year	(1,802,000,000)			(1,509,000,000)
Long-term debt	19,362,000,000			17,623,000,000
Long-term debt to financing trusts	648,000,000			648,000,000
Total long-term debt to financing trusts	648,000,000	[1]		648,000,000	[1]
ComEd Financing Three Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	6.35%	[1]
Long-term debt to financing trusts	206,000,000	[1]		206,000,000	[1]
PECO Trust Three Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	7.38%	[1]
Long-term debt to financing trusts	81,000,000	[1]		81,000,000	[1]
PECO Trust Four Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	5.75%	[1]
Long-term debt to financing trusts	103,000,000	[1]		103,000,000	[1]
BGE Trust Member [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	6.20%	[1]
Long-term debt to financing trusts	258,000,000	[1]		258,000,000	[1]
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Maximum interest rate on long-term debt	6.50%
Long-term Debt, Gross	1,150,000,000		1,150,000,000.00	0
Secured Debt [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	1.20%	[2],[3]
Maximum interest rate on long-term debt	6.45%	[2],[3]
Long-term Debt, Gross	8,079,000,000	[2],[3]		7,746,000,000	[2],[3]
Unsecured Debt [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	2.80%
Maximum interest rate on long-term debt	6.35%
Long-term Debt, Gross	1,750,000,000			1,750,000,000
Rate Stabilization Bonds [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	5.72%
Maximum interest rate on long-term debt	5.82%
Long-term Debt, Gross	195,000,000			265,000,000
Senior Notes [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	2.00%
Maximum interest rate on long-term debt	7.60%
Long-term Debt, Gross	7,071,000,000			7,571,000,000
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	3.25%
Maximum interest rate on long-term debt	3.35%
Long-term Debt, Gross	70,000,000			0
Pollution Control Notes [Member]
Debt Instrument [Line Items]
Maximum interest rate on long-term debt	4.10%
Long-term Debt, Gross	0			20,000,000
Non Recourse Fixed Rate [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	2.33%
Maximum interest rate on long-term debt	6.00%
Long-term Debt, Gross	1,166,000,000			1,077,000,000
Non Recourse Variable Rate [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	2.40625%
Maximum interest rate on long-term debt	5.00%
Long-term Debt, Gross	1,101,000,000			150,000,000
Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	6.95%	[4]
Maximum interest rate on long-term debt	7.825%	[4]
Long-term Debt, Gross	174,000,000	[4]		181,000,000	[4]
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital lease obligations, noncurrent	32,000,000			41,000,000
Due in 2015	3,000,000
Due in 2016	4,000,000
Due in 2018	4,000,000
Due in 2019	5,000,000
Due in 2020	12,000,000
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	8,134,000,000			7,552,000,000
Unamortized debt discount and premium, net	(14,000,000)			11,000,000
Long-term debt (including amounts due within one year)	146,000,000			166,000,000
Long-term debt due within one year	(614,000,000)			(561,000,000)
Long-term debt	6,709,000,000			5,645,000,000
Long-term debt to financing trusts	943,000,000			1,523,000,000
Debt and Capital Lease Obligations	7,652,000,000			7,168,000,000
Capital lease obligations, noncurrent	24,000,000			33,000,000
Due in 2015	3,000,000
Due in 2016	4,000,000
Due in 2017	4,000,000
Due in 2018	4,000,000
Due in 2020	4,000,000
Exelon Generation Co L L C [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	2.00%
Maximum interest rate on long-term debt	7.60%
Long-term Debt, Gross	5,771,000,000			6,271,000,000
Exelon Generation Co L L C [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	3.25%
Long-term Debt, Gross	70,000,000			0
Exelon Generation Co L L C [Member] | Pollution Control Notes [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	4.10%
Long-term Debt, Gross	0			20,000,000
Exelon Generation Co L L C [Member] | Non Recourse Fixed Rate [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	2.33%
Maximum interest rate on long-term debt	6.00%
Long-term Debt, Gross	1,166,000,000			1,077,000,000
Exelon Generation Co L L C [Member] | Non Recourse Variable Rate [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	2.40625%
Maximum interest rate on long-term debt	5.00%
Long-term Debt, Gross	1,101,000,000			150,000,000
Exelon Generation Co L L C [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Maximum interest rate on long-term debt	7.825%	[5]
Long-term Debt, Gross	26,000,000	[5]		33,000,000	[5]
Exelon Generation Co L L C [Member] | Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Due in 2019	5,000,000
Exelon Generation Co L L C [Member] | Social Security Administration [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	2.93%
Long-term Debt, Gross	0			1,000,000
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	5,977,000,000			5,694,000,000
Unamortized debt discount and premium, net	(19,000,000)			(19,000,000)
Long-term debt due within one year	(260,000,000)			(617,000,000)
Long-term debt	5,698,000,000			5,058,000,000
Interest rate on long-term debt	6.35%	[6]
Long-term debt to financing trusts	206,000,000			206,000,000
Debt and Capital Lease Obligations	5,698,000,000			5,058,000,000
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	206,000,000	[1]
Commonwealth Edison Co [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	6.95%	[7]
Maximum interest rate on long-term debt	7.4865%	[7]
Long-term Debt, Gross	148,000,000	[7]		148,000,000	[7]
Commonwealth Edison Co [Member] | Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital lease obligations, noncurrent	8,000,000			8,000,000
Due in 2020	1,000,000
Commonwealth Edison Co [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	1.95%	[8],[9]
Maximum interest rate on long-term debt	6.45%	[8],[9]
Long-term Debt, Gross	5,829,000,000	[8],[9]		5,546,000,000	[8],[9]
PECO Energy Co [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	2,250,000,000			2,200,000,000
Unamortized debt discount and premium, net	(4,000,000)			(3,000,000)
Long-term debt	2,246,000,000			1,947,000,000
Long-term debt to financing trusts	184,000,000	[10]		184,000,000	[10]
Long-term debt due within one year	0			(250,000,000)
Debt and Capital Lease Obligations	2,246,000,000			1,947,000,000
PECO Energy Co [Member] | PECO Trust Three Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	7.38%	[10]
Long-term debt to financing trusts	81,000,000	[10]		81,000,000	[10]
PECO Energy Co [Member] | PECO Trust Four Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	5.75%	[10]
Long-term debt to financing trusts	103,000,000	[10]		103,000,000	[10]
PECO Energy Co [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	1.20%	[11],[12]
Maximum interest rate on long-term debt	5.95%	[11],[12]
Long-term Debt, Gross	2,250,000,000	[11],[12]		2,200,000,000	[11],[12]
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	1,945,000,000			2,015,000,000
Unamortized debt discount and premium, net	(3,000,000)			(4,000,000)
Long-term debt	1,867,000,000			1,941,000,000
Long-term debt to financing trusts	258,000,000			258,000,000
Long-term debt due within one year	(75,000,000)			(70,000,000)
Debt and Capital Lease Obligations				2,011,000,000
Long-term debt	1,867,000,000			1,941,000,000
Baltimore Gas and Electric Company [Member] | BGE Trust Member [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	6.20%	[13]
Long-term debt to financing trusts	258,000,000	[13]		258,000,000	[13]
Baltimore Gas and Electric Company [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	2.80%
Maximum interest rate on long-term debt	6.35%
Long-term Debt, Gross	1,750,000,000			1,750,000,000
Baltimore Gas and Electric Company [Member] | Rate Stabilization Bonds [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	5.72%
Maximum interest rate on long-term debt	5.82%
Long-term Debt, Gross	$ 195,000,000			$ 265,000,000

[1] Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets.

[2] Includes first mortgage bonds issued under the ComEd and PECO mortgage indentures securing pollution control bonds and notes.

[3] Substantially all of ComEd’s assets other than expressly excepted property and substantially all of PECO’s assets are subject to the liens of their respective mortgage indentures.

[4] Includes capital lease obligations of $32 million and $41 million at December 31, 2014 and 2013, respectively. Lease payments of $3 million, $4 million, $4 million, $4 million, $5 million and $12 million will be made in 2015, 2016, 2017, 2018, 2019 and thereafter, respectively.

[5] Includes Generation’s capital lease obligations of $24 million and $33 million at December 31, 2014 and 2013, respectively. Generation will make lease payments of $3 million, $4 million, $4 million, $4 million, $5 million and $4 million in 2015, 2016, 2017, 2018, 2019 and thereafter, respectively.

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

[7] Includes ComEd’s capital lease obligations of $8 million at both December 31, 2014 and 2013, respectively. Lease payments of less than $1 million will be made from 2015 through expiration at 2053.

[8] Includes first mortgage bonds issued under the ComEd mortgage indenture securing pollution control bonds and notes.

[9] Substantially all of ComEd’s assets other than expressly excepted property are subject to the lien of its mortgage indenture.

[10] Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within PECO’s Consolidated Balance Sheets.

[11] Includes first mortgage bonds issued under the PECO mortgage indenture securing pollution control bonds and notes.

[12] Substantially all of PECO’s assets are subject to the lien of its mortgage indenture.

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