Significant Accounting Policies Revenue Initial Application Period Cumulative Effect Transition (Details) - USD ($) $ in Millions	3 Months Ended									9 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue											$ 19,168	$ 17,394	$ 16,330
Regulated Operating Revenue											(16,879)	(15,964)	(14,988)
Electric Revenue												0	0
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues	$ 8,814	$ 9,403	$ 8,076	$ 9,693	$ 8,384	$ 8,768	$ 7,665	$ 8,747			35,985	33,565	31,366
Revenue from Contract with Customer, Including Assessed Tax											(62)	207	48
Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												17,360	16,324
Regulated Operating Revenue												(16,171)	(15,036)
Electric Revenue												0	0
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												33,531	31,360
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												34	6
Regulated Operating Revenue												207	48
Electric Revenue												0	0
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												34	6
Revenue from Contract with Customer, Including Assessed Tax												207	48
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Exelon Generation Co L L C [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue											19,169	17,385	16,318
Regulated Operating Revenue												0	0
Electric Revenue												0	0
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates											1,268	1,115	1,439
Revenues	5,069	5,278	4,579	5,512	4,657	4,750	4,216	4,878			20,437	18,500	17,757
Revenue from Contract with Customer, Including Assessed Tax												0	0
Exelon Generation Co L L C [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Exelon Generation Co L L C [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												17,351	16,312
Regulated Operating Revenue												0	0
Electric Revenue												0	0
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												1,115	1,439
Revenues												18,466	17,751
Exelon Generation Co L L C [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Exelon Generation Co L L C [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												34	6
Regulated Operating Revenue												0	0
Electric Revenue												0	0
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												34	6
Revenue from Contract with Customer, Including Assessed Tax												0	0
Exelon Generation Co L L C [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Commonwealth Edison Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue											5,884	5,478	5,263
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates											27	15	15
Revenues	1,373	1,598	1,398	1,512	1,309	1,571	1,357	1,298			5,882	5,536	5,254
Revenue from Contract with Customer, Including Assessed Tax											(29)	43	(24)
Commonwealth Edison Co [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												5,521	5,239
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												15	15
Revenues												5,536	5,254
Commonwealth Edison Co [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												(43)	24
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												0	0
Revenue from Contract with Customer, Including Assessed Tax												43	(24)
PECO Energy Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue											2,469	2,369	2,524
Gas Domestic Regulated Revenue											568	494	462
Operating revenues from affiliates											8	7	8
Revenues	765	757	653	866	729	715	630	796			3,038	2,870	2,994
Revenue from Contract with Customer, Including Assessed Tax											(7)	0	0
PECO Energy Co [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												2,369	2,524
Gas Domestic Regulated Revenue												494	462
Operating revenues from affiliates												7	8
Revenues												2,870	2,994
PECO Energy Co [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												0	0
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												0	0
Revenue from Contract with Customer, Including Assessed Tax												0	0
Baltimore Gas and Electric Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue											2,428	2,384	2,531
Gas Domestic Regulated Revenue											738	652	628
Operating revenues from affiliates											29	16	21
Revenues	799	731	662	977	813	738	674	951			3,169	3,176	3,233
Revenue from Contract with Customer, Including Assessed Tax											(26)	124	53
Baltimore Gas and Electric Company [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												2,484	2,603
Gas Domestic Regulated Revenue												676	609
Operating revenues from affiliates												16	21
Revenues												3,176	3,233
Baltimore Gas and Electric Company [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												(100)	(72)
Gas Domestic Regulated Revenue												(24)	19
Operating revenues from affiliates													0
Revenues												0	0
Revenue from Contract with Customer, Including Assessed Tax												124	53
Pepco Holdings LLC [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electric Revenue											4,609	4,428
Gas Domestic Regulated Revenue											181	161
Operating revenues from affiliates											15	50
Revenues	1,117	1,361	1,076	1,251	1,121	1,310	1,074	1,175			4,805	4,679
Revenue from Contract with Customer, Including Assessed Tax											0	40
Potomac Electric Power Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue											2,233	2,126	2,167
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates											6	6	5
Revenues	531	628	523	557	510	604	514	530			2,239	2,158	2,186
Revenue from Contract with Customer, Including Assessed Tax											0	26	14
Potomac Electric Power Company [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												2,152	2,181
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												6	5
Revenues												2,158	2,186
Potomac Electric Power Company [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												(26)	(14)
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												0	0
Revenue from Contract with Customer, Including Assessed Tax												26	14
Delmarva Power & Light Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue											1,139	1,125	1,128
Gas Domestic Regulated Revenue											181	161	148
Operating revenues from affiliates											8	8	7
Revenues	331	328	289	384	330	327	282	362			1,332	1,300	1,277
Revenue from Contract with Customer, Including Assessed Tax											4	6	(6)
Delmarva Power & Light Company [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												1,131	1,122
Gas Domestic Regulated Revenue												161	148
Operating revenues from affiliates												8	7
Revenues												1,300	1,277
Delmarva Power & Light Company [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												(6)	6
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												0	0
Revenue from Contract with Customer, Including Assessed Tax												6	(6)
Atlantic City Electric Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue											1,237	1,176	1,245
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates											3	2	3
Revenues	$ 254	$ 406	$ 265	$ 310	$ 271	$ 370	$ 270	$ 275			1,236	1,186	1,257
Revenue from Contract with Customer, Including Assessed Tax											(4)	8	9
Atlantic City Electric Company [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												1,184	1,254
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												2	3
Revenues												1,186	1,257
Atlantic City Electric Company [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												(8)	(9)
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												0	0
Revenue from Contract with Customer, Including Assessed Tax												8	$ 9
Successor [Member] | Pepco Holdings LLC [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue										$ 0		0
Regulated Operating Revenue										0		0
Electric Revenue										3,463		4,428
Gas Domestic Regulated Revenue										92		161
Operating revenues from affiliates										45	$ 15	50
Revenues										3,643		4,679
Revenue from Contract with Customer, Including Assessed Tax										43		40
Successor [Member] | Pepco Holdings LLC [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue										0		0
Regulated Operating Revenue										0		0
Electric Revenue										3,506		4,468
Gas Domestic Regulated Revenue										92		161
Operating revenues from affiliates										45		50
Revenues										3,643		4,679
Successor [Member] | Pepco Holdings LLC [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue										0		0
Regulated Operating Revenue										0		0
Electric Revenue										(43)		(40)
Gas Domestic Regulated Revenue										0		0
Operating revenues from affiliates										0		0
Revenues										0		0
Revenue from Contract with Customer, Including Assessed Tax										$ 43		$ 40
Predecessor [Member] | Pepco Holdings LLC [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue									$ 0
Regulated Operating Revenue									0
Electric Revenue									1,122
Gas Domestic Regulated Revenue									57
Operating revenues from affiliates									0
Revenues									1,153
Revenue from Contract with Customer, Including Assessed Tax									(26)
Predecessor [Member] | Pepco Holdings LLC [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue									0
Regulated Operating Revenue									0
Electric Revenue									1,096
Gas Domestic Regulated Revenue									57
Operating revenues from affiliates									0
Revenues									1,153
Predecessor [Member] | Pepco Holdings LLC [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue									0
Regulated Operating Revenue									0
Electric Revenue									26
Gas Domestic Regulated Revenue									0
Operating revenues from affiliates									0
Revenues									0
Revenue from Contract with Customer, Including Assessed Tax									$ (26)