New Accounting Standards Revenue Initial Application Period Cumulative Effect Transition (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue		$ 5,113	$ 4,550
Regulated Operating Revenue		4,570	4,118
Revenues from alternative revenue programs		10	79
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties	[1]	0	0
Revenues		9,693	8,747
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			(10)
Regulated Operating Revenue			(79)
Revenues from alternative revenue programs			79
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			(10)
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			4,560
Regulated Operating Revenue			4,197
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			8,757
Exelon Generation Co L L C [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue		5,114	4,548
Regulated Operating Revenue			0
Revenues from alternative revenue programs			0
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties		398	330
Revenues		5,512	4,878
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			(10)
Regulated Operating Revenue			0
Revenues from alternative revenue programs			0
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			(10)
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			4,558
Regulated Operating Revenue			0
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties			330
Revenues			4,888
Commonwealth Edison Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Revenues from alternative revenue programs		5	14
Electric operating revenues		1,493	1,279
Natural gas operating revenues			0
Revenue from Related Parties		14	5
Revenues		1,512	1,298
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
Regulated Operating Revenue			0
Revenues from alternative revenue programs			14
Electric operating revenues			(14)
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			0
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
Regulated Operating Revenue			0
Electric operating revenues			1,293
Natural gas operating revenues			0
Revenue from Related Parties			5
Revenues			1,298
PECO Energy Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Revenues from alternative revenue programs		(1)	0
Electric operating revenues		633	589
Natural gas operating revenues		232	206
Revenue from Related Parties		2	1
Revenues		866	796
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
Regulated Operating Revenue			0
Revenues from alternative revenue programs			0
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			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
Regulated Operating Revenue			0
Electric operating revenues			589
Natural gas operating revenues			206
Revenue from Related Parties			1
Revenues			796
Baltimore Gas and Electric Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Revenues from alternative revenue programs		(13)	35
Electric operating revenues		654	640
Natural gas operating revenues		330	271
Revenue from Related Parties		6	5
Revenues		977	951
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
Regulated Operating Revenue			0
Revenues from alternative revenue programs			35
Electric operating revenues			(25)
Natural gas operating revenues			(10)
Revenue from Related Parties			0
Revenues			0
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
Regulated Operating Revenue			0
Electric operating revenues			665
Natural gas operating revenues			281
Revenue from Related Parties			5
Revenues			951
Pepco Holdings LLC [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Revenues from alternative revenue programs		18	30
Electric operating revenues		1,151	1,067
Natural gas operating revenues		78	66
Revenue from Related Parties		4	12
Revenues		1,251	1,175
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
Revenues from alternative revenue programs			30
Electric operating revenues			(30)
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			0
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 operating revenues			1,097
Natural gas operating revenues			66
Revenue from Related Parties			12
Revenues			1,175
Potomac Electric Power Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Revenues from alternative revenue programs		19	15
Electric operating revenues		536	514
Natural gas operating revenues			0
Revenue from Related Parties		2	1
Revenues		557	530
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
Regulated Operating Revenue			0
Revenues from alternative revenue programs			15
Electric operating revenues			(15)
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			0
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
Regulated Operating Revenue			0
Electric operating revenues			529
Natural gas operating revenues			0
Revenue from Related Parties			1
Revenues			530
Delmarva Power and Light Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Revenues from alternative revenue programs		1	9
Electric operating revenues		303	285
Natural gas operating revenues		78	66
Revenue from Related Parties		2	2
Revenues		384	362
Delmarva Power and 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
Regulated Operating Revenue			0
Revenues from alternative revenue programs			9
Electric operating revenues			(9)
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			0
Delmarva Power and 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
Regulated Operating Revenue			0
Electric operating revenues			294
Natural gas operating revenues			66
Revenue from Related Parties			2
Revenues			362
Atlantic City Electric Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Revenues from alternative revenue programs		(2)	6
Electric operating revenues		311	268
Natural gas operating revenues			0
Revenue from Related Parties		1	1
Revenues		$ 310	275
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
Regulated Operating Revenue			0
Revenues from alternative revenue programs			6
Electric operating revenues			(6)
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			0
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
Regulated Operating Revenue			0
Electric operating revenues			274
Natural gas operating revenues			0
Revenue from Related Parties			1
Revenues			$ 275

[1] Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s 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 and Comprehensive Income.