Related Party Transactions - Related Party Transactions included in Consolidated Income Statement (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Related Party Transaction [Line Items]
Operating revenues from affiliates				$ 7		$ 10		$ 9
Interest expense to affiliates, net				36		41		41
Income (Loss) from Equity Method Investments				(32)		(24)		(7)
Cash dividends paid to parent				1,236		1,166		1,105
PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[1]			1		1		1
Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[1]			4		4		4
Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				2		5		4
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions				1		1		1
ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				14		13		13
PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				6		6		6
PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				6		6		6
BGE Capital Trust II Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				10		16		16
Qualifying Facilities And Domestic Power Projects Affiliate [Member]
Related Party Transaction [Line Items]
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions				(33)		(25)		(8)
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				1,115		1,439		749
Related Party Transaction, Purchases from Related Party				19		12		14
Operating and maintenance from affiliates				697		663		620
Interest expense to affiliates, net				39		39		43
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions				(33)		(25)		(8)
Income (Loss) from Equity Method Investments								(8)
Cash distribution paid to member				659		922		2,474
Cash contributions received from affiliates				102		142		47
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[2]			121		47		18
Related Party Transaction, Purchases from Related Party				13		0		0
Operating and maintenance from affiliates	[3]			7		7		4
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[4]			138		290		224
Operating and maintenance from affiliates	[3]			1		3		2
Interest expense to affiliates, net				1		0		0
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[5]			388		608		502
Related Party Transaction, Purchases from Related Party				9		12		14
Operating and maintenance from affiliates	[3]			1		1		0
Exelon Generation Co L L C [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				255	[6]	295	[7]	0	[6]
Operating and maintenance from affiliates				0		1		0
Exelon Generation Co L L C [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				179	[8]	154	[6]	0	[8]
Exelon Generation Co L L C [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				29	[7]	37	[8]	0	[7]
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				1		2		1
Operating and maintenance from affiliates	[9]			689		650		614
Capitalized costs	[9]			98		98		76
Exelon Generation Co L L C [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				4		6		4
Related Party Transaction, Purchases from Related Party				(3)		0		0
Operating and maintenance from affiliates				(2)		0		0
Exelon Generation Co L L C [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net	[10]			37		39		43
Cash distribution paid to member				659		922		2,474
Cash contributions received from affiliates				102		142		47
Exelon Generation Co L L C [Member] | Qualifying Facilities And Domestic Power Projects Affiliate [Member]
Related Party Transaction [Line Items]
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions				(33)		(25)		(8)
Exelon Generation Co L L C [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates				1		1		0
Exelon Generation Co L L C [Member] | Potomac Capital Investment Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				1		0		0
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				15		15		4
Related Party Transaction, Purchases from Related Party				108		47		18
Operating and maintenance from affiliates				270		227		195
Interest expense to affiliates, net				13		13		13
Income (Loss) from Equity Method Investments				0		0		0
Cash dividends paid to parent				422		369		299
Proceeds from Contributions from Parent				651		315		202
Commonwealth Edison Co [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				0		1		0
Operating and maintenance from affiliates				0		1		0
Commonwealth Edison Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				0		1		0
Operating and maintenance from affiliates				0		1		0
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				9		7		4
Related Party Transaction, Purchases from Related Party	[11]			108		47		18
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				6		6		0
Operating and maintenance from affiliates	[12]			270		225		195
Capitalized costs	[12]			118		112		103
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				13		13		13
Commonwealth Edison Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent				422		369		299
Proceeds from Contributions from Parent				651		315		202
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				7		8		2
Related Party Transaction, Purchases from Related Party				135		287		220
Operating and maintenance from affiliates				149		146		110
Interest expense to affiliates, net				11		12		12
Income (Loss) from Equity Method Investments				0		0		0
Cash dividends paid to parent				288		277		279
Proceeds from Contributions from Parent				16		18		16
PECO Energy Co [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				0		1		0
Operating and maintenance from affiliates				0		1		0
PECO Energy Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				1		1		0
Operating and maintenance from affiliates				1		1		0
PECO Energy Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[13]			1		3		2
Related Party Transaction, Purchases from Related Party	[14]			135		287		220
Operating and maintenance from affiliates				2		2		3
Interest income from affiliates, net				(1)		0		0
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				5		3		0
Operating and maintenance from affiliates	[15]			146		142		107
Capitalized costs	[15]			59		57		40
PECO Energy Co [Member] | PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				6		6		6
PECO Energy Co [Member] | PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				6		6		6
PECO Energy Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent				288		277		279
Proceeds from Contributions from Parent				16		18		16
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				16		21		14
Related Party Transaction, Purchases from Related Party				384		604		498
Operating and maintenance from affiliates				153		132		118
Interest expense to affiliates, net				10		16		16
Income (Loss) from Equity Method Investments				0		0		0
Cash dividends paid to parent				198		179		158
Proceeds from Contributions from Parent				184		61		7
Baltimore Gas and Electric Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				0		1		0
Operating and maintenance from affiliates				0		1		0
Baltimore Gas and Electric Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				1		1		0
Operating and maintenance from affiliates				1		1		0
Baltimore Gas and Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[16]			10		13		14
Related Party Transaction, Purchases from Related Party	[17]			384		604		498
Baltimore Gas and Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				5		6		0
Operating and maintenance from affiliates	[18]			152		130		118
Capitalized costs	[18]			54		36		28
Baltimore Gas and Electric Company [Member] | BGE Capital Trust II Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				10		16		16
Baltimore Gas and Electric Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent				198		179		158
Proceeds from Contributions from Parent				184		61		7
Pepco Holdings LLC [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party		$ 0						0
Pepco Holdings LLC [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			$ 45	50
Related Party Transaction, Purchases from Related Party			486	463
Operating and maintenance from affiliates			89	150
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions			0	1
Income (Loss) from Equity Method Investments			0	(1)
Cash distribution paid to member			273	311
Cash dividends paid to parent			0	0
Proceeds from Contributions from Parent			1,251	758
Pepco Holdings LLC [Member] | Exelon Generation Co LLC Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0
Related Party Transaction, Purchases from Related Party			486	463
Pepco Holdings LLC [Member] | Exelon Business Services Co Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			44	48
Operating and maintenance from affiliates	[19]		86	145
Pepco Holdings LLC [Member] | Other Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates			3	5
Pepco Holdings LLC [Member] | Exelon Corporation Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent			273	311
Proceeds from Contributions from Parent			1,251	758
Pepco Holdings LLC [Member] | PHI Service Co Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			$ 0	2
Potomac Electric Power Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				6		5		5
Related Party Transaction, Purchases from Related Party				255		295		0
Operating and maintenance from affiliates				58		35		4
Income (Loss) from Equity Method Investments				0		0		0
Cash dividends paid to parent				133		136		146
Proceeds from Contributions from Parent				161		187		112
Potomac Electric Power Company [Member] | Corporate, Non-Segment [Member]
Related Party Transaction [Line Items]
Operating and maintenance				248		302		266
Potomac Electric Power Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[20]			0		1		0
Related Party Transaction, Purchases from Related Party	[21]			255		295		0
Potomac Electric Power Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[22]			53		31		0
Potomac Electric Power Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent				133		136		146
Proceeds from Contributions from Parent				161		187		112
Potomac Electric Power Company [Member] | Pepco Energy Services Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance	[23]			29		39		26
Potomac Electric Power Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				6		4		5
Operating and maintenance from affiliates	[22]			5		4		4
Operating and maintenance	[22]			219		263		240
Delmarva Power and Light Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				8		7		6
Related Party Transaction, Purchases from Related Party				179		154		0
Operating and maintenance from affiliates				32		19		1
Income (Loss) from Equity Method Investments				0		0		0
Cash dividends paid to parent				112		54		92
Proceeds from Contributions from Parent				0		152		75
Delmarva Power and Light Company [Member] | Corporate, Non-Segment [Member]
Related Party Transaction [Line Items]
Operating and maintenance				174		202		182
Delmarva Power and Light Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	[24]			179		154		0
Delmarva Power and Light Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[25]			31		18		0
Delmarva Power and Light Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				2		2		1
Operating and maintenance from affiliates				1		1		1
Delmarva Power and Light Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent				112		54		92
Proceeds from Contributions from Parent				0		152		75
Delmarva Power and Light Company [Member] | Pepco Energy Services Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance	[26]			9		8		3
Delmarva Power and Light Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				6		5		5
Operating and maintenance	[25]			165		194		179
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				2		3		4
Related Party Transaction, Purchases from Related Party				29		37		0
Operating and maintenance from affiliates				28		18		3
Income (Loss) from Equity Method Investments				0		0		0
Cash dividends paid to parent				68		63		12
Proceeds from Contributions from Parent				0		139		95
Atlantic City Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	[27]			29		37		0
Atlantic City Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[28]			25		15		0
Atlantic City Electric Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				1		1		2
Operating and maintenance from affiliates				3		3		3
Atlantic City Electric Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent				68		63		12
Cash contributions received from affiliates				0		139		95
Atlantic City Electric Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				1		2		2
Operating and maintenance	[28]			$ 135		$ 155		$ 143

[1] The intersegment profit associated with the sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations. See Note 3—Regulatory Matters for additional information.

[2] 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.

[3] Generation requires electricity for its own use at its generating stations. Generation purchases electricity and distribution and transmission services from PECO and BGE and only distribution and transmission services from ComEd for the delivery of electricity to its generating stations.

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

[5] 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.

[6] (d)Generation provides electric supply to Pepco under contracts executed through Pepco's competitive procurement process approved by the MDPSC and DCPSC. See Note 3—Regulatory Matters for additional information.

[7] Generation provides electric supply to ACE under contracts executed through ACE's competitive procurement process. See Note 3—Regulatory Matters for additional information.

[8] (e)Generation provides a portion of DPL's energy requirements under its MDPSC and DPSC approved market based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.

[9] Generation receives a variety of corporate support services from BSC and PHISCO, 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 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.

[11] 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 12—Derivative Financial Instruments for additional information.

[12] 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.

[13] PECO provides energy to Generation for Generation’s own use.

[14] 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.

[15] 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.

[16] BGE provides energy to Generation for Generation’s own use.

[17] 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.

[18] 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.

[19] PHI receives a variety of corporate support services from BSC and PHISCO, 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.

[20] Pepco provides energy to Generation for Generation’s own use.

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

[22] Pepco receives a variety of corporate support services from BSC and PHISCO, 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.

[23] PES performs underground transmission, distribution construction and maintenance services, including services that are treated as capital costs, for Pepco.

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

[25] DPL receives a variety of corporate support services from BSC and PHISCO, 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.

[26] PES performs underground transmission construction services, including services that are treated as capital costs, for DPL.

[27] (a)ACE purchases electric supply from Generation under contracts executed through its competitive procurement process. See Note 3—Regulatory Matters for additional information.

[28] ACE receives a variety of corporate support services from BSC and PHISCO, 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.