Related Party Transactions - Related Party Transactions included in Consolidated Balance Sheet (Details) - USD ($) $ in Millions			12 Months Ended
		Apr. 01, 2014	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Total payables to affiliates (current)			$ (8)	$ (8)
Long-term debt to financing trusts			$ 641	641
Required purchases of power from CENG's nuclear plants not sold to third parties			85.00%
Purchase of nuclear output of CENG			50.01%
Purchase of nuclear output by EDF			49.99%
Accounts Payable, Related Parties, Current			$ 8	8
ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			205	205
Accounts Payable, Related Parties, Current			4	4
PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			81	81
Accounts Payable, Related Parties, Current			1	1
PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			103	103
BGE Capital Trust II [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			252	252
Accounts Payable, Related Parties, Current			3	3
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			83	113
Total payables to affiliates (current)			0	(556)
Due to Affiliate, Noncurrent			2,577	2,880
Required purchases of power from CENG's nuclear plants not sold to third parties		85.00%
Purchase of nuclear output by EDF		49.99%
Accounts Payable, Related Parties, Current			104	107
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	[1]		15	43
Due to Affiliate, Noncurrent	[2]		2,172	2,389
Accounts Payable, Related Parties, Current			9	12
Exelon Generation Co L L C [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			1	1
Accounts Payable, Related Parties, Current			1	0
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	[3]		36	29
Due to Affiliate, Noncurrent	[2]		405	490
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	[4]		31	40
Exelon Generation Co L L C [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)			(1,252)	(556)
Long Term Debt To Affiliate			933	943
Accounts Payable, Related Parties, Current	[5]		16	12
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Due to Affiliate, Noncurrent	[6]		0	1
Accounts Payable, Related Parties, Current	[6]		78	83
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Prepaid voluntary employee beneficiary association trust	[7]		0	1
Accounts Payable, Related Parties, Current			52	66
Baltimore Gas and Electric Company [Member] | BGE Capital Trust II [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			252	252
Accounts Payable, Related Parties, Current			3	3
Baltimore Gas and Electric Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current			0	1
Baltimore Gas and Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[8]		31	40
Baltimore Gas and Electric Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[7]		1	5
Baltimore Gas and Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[9]		17	17
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			2	3
Total receivable from affiliates (noncurrent)			405	490
Long-term debt to financing trusts			184	184
Prepaid voluntary employee beneficiary association trust	[10]		2	3
Accounts Payable, Related Parties, Current			55	52
PECO Energy Co [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)			2	2
PECO Energy Co [Member] | PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			81	81
Accounts Payable, Related Parties, Current			1	1
PECO Energy Co [Member] | PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			103	103
PECO Energy Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)			0	1
PECO Energy Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)	[11]		405	490
Accounts Payable, Related Parties, Current	[12]		36	29
PECO Energy Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current			1	2
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[13]		17	20
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			199	14
Total receivable from affiliates (noncurrent)			2,172	2,571
Prepaid voluntary employee beneficiary association trust	[14]		11	13
Accounts Payable, Related Parties, Current			62	84
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts			205	205
Accounts Payable, Related Parties, Current			4	4
Commonwealth Edison Co [Member] | Voluntary Employee Beneficiary Association Trust [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			2	2
Commonwealth Edison Co [Member] | Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)				12
Commonwealth Edison Co [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	[15]		188
Total receivable from affiliates (noncurrent)	[15]		0	182
Commonwealth Edison Co [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current			2	2
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)			9
Total receivable from affiliates (noncurrent)	[16]		2,172	2,389
Accounts Payable, Related Parties, Current	[17]		15	43
Commonwealth Edison Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current			2	3
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[18]		$ 39	$ 32

[1] Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs to ComEd. In addition, Generation had revenue from ComEd associated with the settled portion of the financial swap contract established as part of the Illinois Settlement. See Note 3—Regulatory Matters for additional information.

[2] Generation has long-term payables to ComEd and PECO as a result of the nuclear decommissioning contractual construct whereby, to the extent NDT funds are greater than the underlying ARO at the end of decommissioning, such amounts are due back to ComEd and PECO, as applicable, for payment to their respective customers. See Note 16—Asset Retirement Obligations

[3] Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has five-year and ten-year agreements with PECO to sell non-solar and solar AECs, respectively. See Note 3—Regulatory Matters for additional information.

[4] Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.

[5] The balance consists of interest owed to Exelon Corporation related to the senior unsecured notes, as well as, expense related to certain invoices Exelon Corporation processed on behalf of Generation.

[6] Generation receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.

[7] The voluntary employee benefit association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for BGE’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. The prepayment is included in other current assets.

[8] BGE procures a portion of its electricity and gas supply requirements from Generation under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.

[9] BGE receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.

[10] The voluntary employee beneficiary association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for PECO’s contributions to the plans, being higher than actual claim expense incurred by the plans over time.

[11] PECO has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct, whereby, to the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to PECO for payment to PECO’s customers.

[12] PECO purchases electric supply from Generation under contracts executed through its competitive procurement process. In addition, PECO has five-year and ten-year agreements with Generation to purchase non-solar and solar AECs, respectively. See Note 3—Regulatory Matters for additional information on AECs.

[13] PECO receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.

[14] The voluntary employee benefit association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for ComEd’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. The prepayment is included in other current assets.

[15] Represents indemnification from Exelon Corporate related to the like-kind exchange transaction.

[16] ComEd has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct for generating facilities previously owned by ComEd. To the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to ComEd for payment to ComEd’s customers.

[17] ComEd procures a portion of its electricity supply requirements from Generation under an ICC-approved RFP contract. ComEd also purchases RECs from Generation. In addition, purchased power expense includes the settled portion of the financial swap contract with Generation, which expired in 2013. See Note 3—Regulatory Matters and Note 13—Derivative Financial Instruments for additional information.

[18] ComEd receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.