Related Party Transactions - Related Party Transactions included in Consolidated Income Statement (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Operating revenues from affiliates				$ 0	$ 0
Interest expense to affiliates, net			$ 25	36	41
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions			(28)	(32)	(24)
Equity in earnings (losses) of unconsolidated affiliates			(28)	(32)	(24)
Cash dividends paid to parent			1,332	1,236	1,166
Corporate, Non-Segment [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			(1)	7	10
Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[1]		(2)	0
PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[1]		0	1	1
Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[1]		0	4	4
Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[1]		0	0	0
ComEd Financing III Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			13	14	13
PECO Trust III Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			6	6	6
PECO Trust IV 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			0	10	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			(29)	(33)	(25)
Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	2	5
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions			1	1	1
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1,268	1,115	1,439
Related Party Transaction, Purchases from Related Party			14	19	12
Operating and maintenance from affiliates			661	697	663
Interest expense to affiliates, net			36	39	39
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions			(30)	(33)	(25)
Equity in earnings (losses) of unconsolidated affiliates			(30)	(33)	(25)
Cash distribution paid to member			1,001	659	922
Cash contributions received from affiliates			155	102	142
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[2]		523	121	47
Related Party Transaction, Purchases from Related Party			(6)	13	0
Operating and maintenance from affiliates	[3]		7	7	7
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[4]		128	138	290
Operating and maintenance from affiliates	[3]		2	1	3
Interest expense to affiliates, net			0	1	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]		260	388	608
Related Party Transaction, Purchases from Related Party			20	9	12
Operating and maintenance from affiliates	[3]		2	1	1
Exelon Generation Co L L C [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[6]		206	255	295
Operating and maintenance from affiliates			1	0	1
Exelon Generation Co L L C [Member] | Delmarva Power & Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[7]		120	179	154
Exelon Generation Co L L C [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[8]		29	29	37
Exelon Generation Co L L C [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates			1	1	1
Exelon Generation Co L L C [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net	[9]		36	37	39
Cash distribution paid to member			1,001	659	922
Cash contributions received from affiliates			155	102	142
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			2	1	2
Operating and maintenance from affiliates	[10]		652	689	650
Capitalized costs	[10]		67	98	98
Exelon Generation Co L L C [Member] | Potomac Capital Investment Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			0	1	0
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			(30)	(33)	(25)
Exelon Generation Co L L C [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			0	4	6
Related Party Transaction, Purchases from Related Party			0	(3)	0
Operating and maintenance from affiliates			(4)	(2)	0
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			27	15	15
Related Party Transaction, Purchases from Related Party			529	108	47
Operating and maintenance from affiliates			267	270	227
Interest expense to affiliates, net			13	13	13
Equity in earnings (losses) of unconsolidated affiliates			0	0	0
Cash dividends paid to parent			459	422	369
Proceeds from Contributions from Parent			500	651	315
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			9	9	7
Related Party Transaction, Purchases from Related Party	[11]		529	108	47
Commonwealth Edison Co [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			10	0	1
Operating and maintenance from affiliates			1	0	1
Commonwealth Edison Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	1
Operating and maintenance from affiliates			1	0	1
Commonwealth Edison Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent			459	422	369
Proceeds from Contributions from Parent			500	651	315
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			7	6	6
Operating and maintenance from affiliates	[12]		265	270	225
Capitalized costs	[12]		135	118	112
Commonwealth Edison Co [Member] | ComEd Financing III Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			13	13	13
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			8	7	8
Related Party Transaction, Purchases from Related Party			126	135	287
Operating and maintenance from affiliates			156	149	146
Interest expense to affiliates, net			14	11	12
Equity in earnings (losses) of unconsolidated affiliates			0	0	0
Cash dividends paid to parent			306	288	277
Proceeds from Contributions from Parent			89	16	18
PECO Energy Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[13]		2	1	3
Related Party Transaction, Purchases from Related Party	[14]		126	135	287
Operating and maintenance from affiliates			2	2	2
Interest income from affiliates, net			0	(1)	0
PECO Energy Co [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	1
Operating and maintenance from affiliates			7	0	1
PECO Energy Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	1	1
Operating and maintenance from affiliates			1	1	1
PECO Energy Co [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	0
PECO Energy Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			2	0	0
Cash dividends paid to parent			306	288	277
Proceeds from Contributions from Parent			89	16	18
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			3	5	3
Operating and maintenance from affiliates	[15]		146	146	142
Capitalized costs	[15]		64	59	57
PECO Energy Co [Member] | PECO Trust III Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			6	6	6
PECO Energy Co [Member] | PECO Trust IV Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			6	6	6
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			29	16	21
Related Party Transaction, Purchases from Related Party			257	384	604
Operating and maintenance from affiliates			162	153	132
Interest expense to affiliates, net			0	10	16
Equity in earnings (losses) of unconsolidated affiliates			0	0	0
Cash dividends paid to parent			209	198	179
Proceeds from Contributions from Parent			109	184	61
Baltimore Gas and Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[16]		22	10	13
Related Party Transaction, Purchases from Related Party	[17]		257	384	604
Operating and maintenance from affiliates			3	0	0
Baltimore Gas and Electric Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	1
Operating and maintenance from affiliates			1	0	1
Baltimore Gas and Electric Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	1	1
Operating and maintenance from affiliates			1	1	1
Baltimore Gas and Electric Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent			209	198	179
Proceeds from Contributions from Parent			109	184	61
Baltimore Gas and Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			5	5	6
Operating and maintenance from affiliates	[18]		157	152	130
Capitalized costs	[18]		79	54	36
Baltimore Gas and Electric Company [Member] | BGE Capital Trust II Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			0	10	16
Pepco Holdings LLC [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			15	50
Related Party Transaction, Purchases from Related Party			355	463
Operating and maintenance from affiliates			152	150
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions			1	1
Equity in earnings (losses) of unconsolidated affiliates			1	1
Cash distribution paid to member			326	311
Proceeds from Contributions from Parent			385	758
Pepco Holdings LLC [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates		$ 45	15	50
Related Party Transaction, Purchases from Related Party		486
Operating and maintenance from affiliates		89	152	150
Capitalized costs		0	181	0
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions		0
Equity in earnings (losses) of unconsolidated affiliates		0
Cash distribution paid to member		273
Proceeds from Contributions from Parent		1,251
Pepco Holdings LLC [Member] | Exelon Generation Co LLC Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates		1	2	0
Related Party Transaction, Purchases from Related Party		486	355	463
Pepco Holdings LLC [Member] | PHI Service Co Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates		0	1	2
Capitalized costs	[19]	0	79	0
Pepco Holdings LLC [Member] | Exelon Corporation Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent		1,251	326	311
Proceeds from Contributions from Parent		273	385	758
Pepco Holdings LLC [Member] | Exelon Business Services Co Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates		44	12	48
Operating and maintenance from affiliates	[19]	86	147	145
Capitalized costs	[19]	0	102	0
Pepco Holdings LLC [Member] | Other Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates		3	5	5
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions		$ 0	1	0
Potomac Electric Power Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			6	6	5
Related Party Transaction, Purchases from Related Party			206	255	295
Operating and maintenance from affiliates			226	58	35
Capitalized costs			72	0	0
Equity in earnings (losses) of unconsolidated affiliates			0	0	0
Cash dividends paid to parent			169	133	136
Proceeds from Contributions from Parent			166	161	187
Potomac Electric Power Company [Member] | Corporate, Non-Segment [Member]
Related Party Transaction [Line Items]
Operating and maintenance			0	248	302
Potomac Electric Power Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[20]		1	0	1
Related Party Transaction, Purchases from Related Party	[21]		206	255	295
Potomac Electric Power Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			4	6	4
Operating and maintenance from affiliates	[22],[23]		137	5	4
Operating and maintenance	[22],[23]		0	219	263
Capitalized costs	[23]		32	0	0
Potomac Electric Power Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent			169	133	136
Proceeds from Contributions from Parent			166	161	187
Potomac Electric Power Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	0
Operating and maintenance from affiliates	[23]		89	53	31
Capitalized costs	[23]		40	0	0
Potomac Electric Power Company [Member] | Pepco Energy Services Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance	[24]		0	29	39
Delmarva Power & Light Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			8	8	7
Related Party Transaction, Purchases from Related Party			120	179	154
Operating and maintenance from affiliates			162	32	19
Capitalized costs			53	0	0
Equity in earnings (losses) of unconsolidated affiliates			0	0	0
Cash dividends paid to parent			96	112	54
Proceeds from Contributions from Parent			150	0	152
Delmarva Power & Light Company [Member] | Corporate, Non-Segment [Member]
Related Party Transaction [Line Items]
Operating and maintenance			0	174	202
Delmarva Power & Light Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	[25]		120	179	154
Delmarva Power & Light Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	0
Delmarva Power & Light Company [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	0
Delmarva Power & Light Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			4	6	5
Operating and maintenance from affiliates	[26],[27]		111	0	0
Operating and maintenance	[26],[27]		0	165	194
Capitalized costs	[26]		25	0	0
Delmarva Power & Light Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent			96	112	54
Proceeds from Contributions from Parent			150	0	152
Delmarva Power & Light Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	0
Operating and maintenance from affiliates	[26]		51	31	18
Capitalized costs	[26]		28	0	0
Delmarva Power & Light Company [Member] | Pepco Energy Services Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance	[28]		0	9	8
Delmarva Power & Light Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	2	2
Operating and maintenance from affiliates			0	1	1
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			3	2	3
Related Party Transaction, Purchases from Related Party			29	29	37
Operating and maintenance from affiliates			142	28	18
Capitalized costs			41	0	0
Equity in earnings (losses) of unconsolidated affiliates			0	0	0
Cash dividends paid to parent			59	68	63
Proceeds from Contributions from Parent			67	0	139
Atlantic City Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	[29]		29	29	37
Atlantic City Electric Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			2	1	2
Operating and maintenance from affiliates	[30],[31]		98	0	0
Operating and maintenance	[30],[31]		0	135	155
Capitalized costs	[30]		21	0	0
Atlantic City Electric Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent			59	68	63
Cash contributions received from affiliates			67	0	139
Atlantic City Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[30]		42	25	15
Capitalized costs	[30]		20	0	0
Atlantic City Electric Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	1	1
Operating and maintenance from affiliates			$ 2	$ 3	$ 3

[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 authoritative guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations. See Note 4—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 and ZECs to ComEd.

[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.

[5] Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs.

[6] Generation provides electric supply to Pepco under contracts executed through Pepco's competitive procurement process approved by the MDPSC and DCPSC.

[7] Generation provides a portion of DPL's energy requirements under its MDPSC and DPSC approved market based SOS and gas commodity programs.

[8] Generation provides electric supply to ACE under contracts executed through ACE's competitive procurement process.

[9] 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.

[10] 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.

[11] ComEd procures a portion of its electricity supply requirements from Generation under an ICC-approved RFP contract. ComEd also purchases RECs and ZECs from Generation.

[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.

[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.

[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 supply requirements from Generation under its MDPSC and DCPSC approved market based SOS commodity programs.

[22] Due to the PHI entities' system conversion to Exelon's accounting systems on January 1, 2018, corporate support services received from PHISCO are reported in Operating and maintenance from affiliates in 2018.

[23] 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.

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

[25] 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.

[26] 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.

[27] Due to the PHI entities' system conversion to Exelon's accounting systems on January 1, 2018, corporate support services received from PHISCO are reported in Operating and maintenance from affiliates in 2018.

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

[29] ACE purchases electric supply from Generation under contracts executed through its competitive procurement process.

[30] 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.

[31] Due to the PHI entities' system conversion to Exelon's accounting systems on January 1, 2018, corporate support services received from PHISCO are reported in Operating and maintenance from affiliates in 2018.