Debt and Credit Agreements - Summary of Outstanding Long-term Debt (Details) - USD ($)		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Jun. 30, 2014
Debt Instrument [Line Items]
Maximum interest rate on long-term debt		3.95%
Long-term Debt, Gross		$ 25,113,000,000	$ 20,864,000,000
Unamortized debt discount and premium, net		(63,000,000)	(37,000,000)
Long-term debt (including amounts due within one year) (a)		275,000,000	333,000,000
Fair value hedge carrying value adjustment, net		0	4,000,000
Long-term debt due within one year		(1,500,000,000)	(1,802,000,000)
Long-term debt		23,645,000,000	19,212,000,000
Long-term debt to financing trusts	[1]	641,000,000	641,000,000
Total long-term debt to financing trusts		648,000,000	648,000,000
Unamortized Debt Issuance Expense	[2]	$ (180,000,000)	(150,000,000)
ComEd Financing Three Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[1]	6.35%
Long-term debt to financing trusts	[1]	$ 206,000,000	206,000,000
PECO Trust Three Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[1]	7.38%
Long-term debt to financing trusts	[1]	$ 81,000,000	81,000,000
PECO Trust Four Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[1]	5.75%
Long-term debt to financing trusts	[1]	$ 103,000,000	103,000,000
BGE Trust Member [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[1]	6.20%
Long-term debt to financing trusts	[1]	$ 258,000,000	258,000,000
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	$ 1,150,000,000.00
Secured Debt [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	[3]	1.20%
Maximum interest rate on long-term debt	[3]	6.45%
Long-term Debt, Gross	[3]	$ 9,019,000,000	8,079,000,000
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		$ 120,000,000	195,000,000
Senior Notes [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		1.55%
Maximum interest rate on long-term debt		7.60%
Long-term Debt, Gross		$ 9,803,000,000	7,071,000,000
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		3.15%
Maximum interest rate on long-term debt		3.35%
Long-term Debt, Gross		$ 127,000,000	70,000,000
Pollution Control Notes [Member]
Debt Instrument [Line Items]
Maximum interest rate on long-term debt		2.70%
Long-term Debt, Gross		$ 435,000,000	0
Non Recourse Fixed Rate [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		2.293%
Maximum interest rate on long-term debt		6.00%
Long-term Debt, Gross		$ 1,162,000,000	1,166,000,000
Non Recourse Variable Rate [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		2.418%
Maximum interest rate on long-term debt		5.00%
Long-term Debt, Gross		$ 1,058,000,000	1,101,000,000
Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	[4]	1.43%
Maximum interest rate on long-term debt	[4]	7.825%
Long-term Debt, Gross	[4],[5]	$ 314,000,000	174,000,000
Unamortized Debt Issuance Expense	[2]	(7,000,000)	(7,000,000)
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital lease obligations, noncurrent		$ 29,000,000	32,000,000
Due in 2015
Due in 2016		$ 4,000,000
Due in 2017		4,000,000
Due in 2018		5,000,000
Due in 2019		4,000,000
Due in 2020		8,000,000
Software License Arrangement [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 111,000,000
contract Payments Junior Subordinate Debt [Member]
Debt Instrument [Line Items]
Maximum interest rate on long-term debt		2.50%
Long-term Debt, Gross		$ 64,000,000	108,000,000
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		8,919,000,000	8,134,000,000
Unamortized debt discount and premium, net		(17,000,000)	(14,000,000)
Long-term debt (including amounts due within one year) (a)		127,000,000	146,000,000
Long-term debt due within one year		(90,000,000)	(614,000,000)
Long-term debt		7,936,000,000	6,639,000,000
Long-term debt to financing trusts		933,000,000	943,000,000
Debt and Capital Lease Obligations		8,869,000,000	7,582,000,000
Capital lease obligations, noncurrent		21,000,000	24,000,000
Due in 2016		4,000,000
Due in 2017		4,000,000
Due in 2018		5,000,000
Due in 2019		4,000,000
Unamortized Debt Issuance Expense	[6]	$ (70,000,000)	(70,000,000)
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		$ 5,971,000,000	5,771,000,000
Exelon Generation Co L L C [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		3.15%
Long-term Debt, Gross			70,000,000
Exelon Generation Co L L C [Member] | Pollution Control Notes [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		2.50%
Long-term Debt, Gross		$ 435,000,000	0
Exelon Generation Co L L C [Member] | Non Recourse Fixed Rate [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		2.293%
Maximum interest rate on long-term debt		6.00%
Long-term Debt, Gross		$ 1,162,000,000	1,166,000,000
Exelon Generation Co L L C [Member] | Non Recourse Variable Rate [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		2.418%
Maximum interest rate on long-term debt		5.00%
Long-term Debt, Gross		$ 1,058,000,000	1,101,000,000
Exelon Generation Co L L C [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt		1.43%
Maximum interest rate on long-term debt	[7]	7.825%
Long-term Debt, Gross	[7],[8]	$ 166,000,000	26,000,000
Long-term debt		100,000,000
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		6,567,000,000	5,977,000,000
Unamortized debt discount and premium, net		(20,000,000)	(19,000,000)
Long-term debt due within one year		(665,000,000)	(260,000,000)
Long-term debt		5,844,000,000	5,665,000,000
Long-term debt to financing trusts		205,000,000	205,000,000
Total long-term debt to financing trusts		206,000,000	206,000,000
Debt and Capital Lease Obligations		5,844,000,000	5,665,000,000
Unamortized Debt Issuance Expense	[9]	$ (38,000,000)	(33,000,000)
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[10]	6.35%
Long-term debt to financing trusts		$ 206,000,000
Total long-term debt to financing trusts		205,000,000	205,000,000
Unamortized Debt Issuance Expense	[9]	$ (1,000,000)	(1,000,000)
Commonwealth Edison Co [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	[11]	6.95%
Maximum interest rate on long-term debt	[11]	7.4865%
Long-term Debt, Gross	[11]	$ 148,000,000	148,000,000
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	[12]	1.95%
Maximum interest rate on long-term debt	[12]	6.45%
Long-term Debt, Gross	[12]	$ 6,419,000,000	5,829,000,000
PECO Energy Co [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		2,600,000,000	2,250,000,000
Unamortized debt discount and premium, net		(5,000,000)	(4,000,000)
Long-term debt		2,280,000,000	2,232,000,000
Long-term debt to financing trusts		184,000,000	184,000,000
Long-term debt due within one year		(300,000,000)	0
Debt and Capital Lease Obligations		2,280,000,000	2,232,000,000
Unamortized Debt Issuance Expense	[13]	$ (15,000,000)	(14,000,000)
PECO Energy Co [Member] | PECO Trust Three Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[14]	7.38%
Long-term debt to financing trusts	[14]	$ 81,000,000	81,000,000
PECO Energy Co [Member] | PECO Trust Four Affiliate [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[14]	5.75%
Long-term debt to financing trusts	[14]	$ 103,000,000	103,000,000
PECO Energy Co [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Minimum interest rate on long-term debt	[15]	1.20%
Maximum interest rate on long-term debt	[15]	5.95%
Long-term Debt, Gross	[15]	$ 2,600,000,000	2,250,000,000
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		1,870,000,000	1,945,000,000
Unamortized debt discount and premium, net		(3,000,000)	(3,000,000)
Long-term debt (including amounts due within one year) (a)			1,932,000,000
Long-term debt		1,480,000,000	1,857,000,000
Long-term debt to financing trusts		252,000,000	252,000,000
Total long-term debt to financing trusts		258,000,000	258,000,000
Long-term debt due within one year		(378,000,000)	(75,000,000)
Long-term debt		1,480,000,000	1,857,000,000
Unamortized Debt Issuance Expense	[16]	$ (9,000,000)	(10,000,000)
Baltimore Gas and Electric Company [Member] | BGE Trust Member [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[17]	6.20%
Long-term debt to financing trusts			252,000,000
Total long-term debt to financing trusts		$ 258,000,000	258,000,000
Unamortized Debt Issuance Expense	[16]	$ (6,000,000)	(6,000,000)
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		$ 120,000,000	$ 195,000,000

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

[2] Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information.

[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 $29 million and $32 million at December 31, 2015 and 2014, respectively. Lease payments of $4 million, $4 million, $4 million, $5 million, $4 million, and $8 million will be made in 2016, 2017, 2018, 2019, 2020 and thereafter, respectively.

[5] Includes financing related to Albany Green Energy, LLC (AGE), which is a consolidated variable interest entity (see Note 2 - Variable Interest Entities for additional information). The agreement is scheduled to expire on November 17, 2017, at a variable rate equal to LIBOR plus 1.25%. As of December 31, 2015, $100 million was outstanding.

[6] Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information.

[7] Includes Generation’s capital lease obligations of $21 million and $24 million at December 31, 2015 and 2014, respectively. Generation will make lease payments of $4 million, $4 million, $4 million, $5 million and $4 million in 2016, 2017, 2018, 2019, 2020, respectively. The capital lease matures in 2020.

[8] Includes financing related to Albany Green Energy, LLC (AGE), which is a consolidated variable interest entity (see Note 2 - Variable Interest Entities for additional information). The agreement is scheduled to expire on November 17, 2017, at a variable rate equal to LIBOR plus 1.25%. As of December 31, 2015, $100 million was outstanding.

[9] Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information.

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

[11] Includes ComEd’s capital lease obligations of $8 million at both December 31, 2015 and 2014, respectively. Lease payments of less than $1 million will be made from 2016 through expiration at 2053.

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

[13] Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information.

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

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

[16] Certain December 31, 2014 balances have been adjusted for the adoption of accounting guidance related to simplifying the presentation of debt costs. See Note 1 - Significant Accounting Policies for additional information.

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