Significant Accounting Policies Revenue Initial Application Period Cumulative Effect Transition (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues	$ 4,971		$ 4,455		$ 14,387		$ 12,955
Rate-regulated utility revenues	4,457		4,259		12,824		12,034
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(25)		54		(41)		191
Operating revenues from affiliates	0	[1]	0	[1]	0	[2]	0
Total operating revenues	9,403		8,768		27,170		25,180
Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			4,456				12,924
Rate-regulated utility revenues			4,313				12,225
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Operating revenues from affiliates			0				0
Total operating revenues			8,769				25,149
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]
Competitive business revenues			0				0
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			(1)				31
Rate-regulated utility revenues			(54)				(191)
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			54				191
Operating revenues from affiliates			0				0
Total operating revenues			(1)				31
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]
Competitive business revenues			0				0
Exelon Generation Co L L C [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues	4,970		4,454		14,389		12,949
Rate-regulated utility revenues			0				0
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			0				0
Operating revenues from affiliates	308		296		979		894
Total operating revenues	5,278		4,750		15,368		13,843
Exelon Generation Co L L C [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			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]
Competitive business revenues			4,455				12,918
Rate-regulated utility revenues			0				0
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Operating revenues from affiliates			296				894
Total operating revenues			4,751				13,812
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]
Competitive business revenues			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]
Competitive business revenues			(1)				31
Rate-regulated utility revenues			0				0
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			0				0
Operating revenues from affiliates			0				0
Total operating revenues			(1)				31
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]
Competitive business revenues			0				0
Commonwealth Edison Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues	1,609		1,552		4,512		4,167
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(15)		16		(27)		48
Operating revenues from affiliates	4		3		23		12
Total operating revenues	1,598		1,571		4,508		4,227
Commonwealth Edison Co [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			1,568				4,215
Natural gas operating revenues			0				0
Operating revenues from affiliates			3				12
Total operating revenues			1,571				4,227
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			(16)				(48)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			16				48
Operating revenues from affiliates			0				0
Total operating revenues			0				0
PECO Energy Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues	697		660		1,886		1,798
Natural gas operating revenues	57		53		382		338
Revenues from alternative revenue programs	1		0		2		0
Operating revenues from affiliates	2		2		5		5
Total operating revenues	757		715		2,275		2,141
PECO Energy Co [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			660				1,798
Natural gas operating revenues			53				338
Operating revenues from affiliates			2				5
Total operating revenues			715				2,141
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			0				0
Operating revenues from affiliates			0				0
Total operating revenues			0				0
Baltimore Gas and Electric Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues	652		626		1,847		1,811
Natural gas operating revenues	79		73		527		438
Revenues from alternative revenue programs	(6)		36		(23)		102
Operating revenues from affiliates	6		3		18		12
Total operating revenues	731		738		2,369		2,363
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			657				1,890
Natural gas operating revenues			78				461
Operating revenues from affiliates			3				12
Total operating revenues			738				2,363
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			(31)				(79)
Natural gas operating revenues			(5)				(23)
Revenues from alternative revenue programs			36				102
Operating revenues from affiliates			0				0
Total operating revenues			0				0
Pepco Holdings LLC [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues	1,340		1,278		3,541		3,376
Natural gas operating revenues	23		18		129		105
Revenues from alternative revenue programs	(5)		2		7		41
Operating revenues from affiliates	3		12		11		35
Total operating revenues	1,361		1,310		3,688		3,557
Pepco Holdings LLC [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			1,280				3,417
Natural gas operating revenues			18				105
Operating revenues from affiliates			12				35
Total operating revenues			1,310				3,557
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			(2)				(41)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			2				41
Operating revenues from affiliates			0				0
Total operating revenues			0				0
Potomac Electric Power Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues	630		600		1,697		1,622
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(4)		3		6		23
Operating revenues from affiliates	2		1		5		4
Total operating revenues	628		604		1,708		1,649
Potomac Electric Power Company [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			603				1,645
Natural gas operating revenues			0				0
Operating revenues from affiliates			1				4
Total operating revenues			604				1,649
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			(3)				(23)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			3				23
Operating revenues from affiliates			0				0
Total operating revenues			0				0
Delmarva Power and Light Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues	302		308		861		851
Natural gas operating revenues	24		18		129		105
Revenues from alternative revenue programs	0		(1)		5		9
Operating revenues from affiliates	2		2		6		6
Total operating revenues	328		327		1,001		971
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			307				860
Natural gas operating revenues			18				105
Operating revenues from affiliates			2				6
Total operating revenues			327				971
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			1				(9)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			(1)				9
Operating revenues from affiliates			0				0
Total operating revenues			0				0
Atlantic City Electric Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues	406		370		983		904
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(1)		0		(4)		9
Operating revenues from affiliates	1		0		2		2
Total operating revenues	$ 406		370		$ 981		915
Atlantic City Electric Company [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			370				913
Natural gas operating revenues			0				0
Operating revenues from affiliates			0				2
Total operating revenues			370				915
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			0				(9)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			0				9
Operating revenues from affiliates			0				0
Total operating revenues			$ 0				$ 0

[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.

[2] 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.