Significant Accounting Policies Revenue Initial Application Period Cumulative Effect Transition (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue	$ 4,305		$ 3,950		$ 9,417		$ 8,500
Regulated Operating Revenue	(3,797)		(3,657)		(8,368)		(7,776)
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(26)		58		(16)		137
Revenue from Related Parties	0	[1]	0	[1]	0	[2]	0	[2]
Revenues	8,076		7,665		17,769		16,413
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			3,908				8,468
Regulated Operating Revenue			(3,715)				(7,913)
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenue from Related Parties			0				0
Revenues			7,623				16,381
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			42				32
Regulated Operating Revenue			(58)				(137)
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			58				137
Revenue from Related Parties			0				0
Revenues			42				32
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	4,306		3,948		9,419		8,495
Regulated Operating Revenue			0				0
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			0				0
Revenue from Related Parties	273		268		671		598
Revenues	4,579		4,216		10,090		9,093
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			3,906				8,463
Regulated Operating Revenue			0				0
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenue from Related Parties			268				598
Revenues			4,174				9,061
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			42				32
Regulated Operating Revenue			0				0
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			0				0
Revenue from Related Parties			0				0
Revenues			42				32
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 operating revenues	(1,410)		(1,336)		(2,903)		(2,615)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(17)		18		(12)		32
Revenue from Related Parties	5		3		19		9
Revenues	1,398		1,357		2,910		2,656
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 operating revenues			(1,354)				(2,647)
Natural gas operating revenues			0				0
Revenue from Related Parties			3				9
Revenues			1,357				2,656
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 operating revenues			(18)				(32)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			18				32
Revenue from Related Parties			0				0
Revenues			0				0
PECO Energy Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0				0
Regulated Operating Revenue			0				0
Electric operating revenues	(556)		(548)		(1,189)		(1,138)
Natural gas operating revenues	(93)		(80)		(325)		(285)
Revenues from alternative revenue programs	2		0		1		0
Revenue from Related Parties	2		2		3		3
Revenues	653		630		1,518		1,426
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 operating revenues			(548)				(1,138)
Natural gas operating revenues			(80)				(285)
Revenue from Related Parties			2				3
Revenues			630				1,426
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 operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			0				0
Revenue from Related Parties			0				0
Revenues			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 operating revenues	(542)		(545)		(1,196)		(1,186)
Natural gas operating revenues	(118)		(94)		(448)		(365)
Revenues from alternative revenue programs	(4)		32		(17)		66
Revenue from Related Parties	6		3		12		8
Revenues	662		674		1,639		1,625
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 operating revenues			(569)				(1,234)
Natural gas operating revenues			(102)				(383)
Revenue from Related Parties			3				8
Revenues			674				1,625
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 operating revenues			(24)				(48)
Natural gas operating revenues			(8)				(18)
Revenues from alternative revenue programs			32				66
Revenue from Related Parties			0				0
Revenues			0				0
Pepco Holdings LLC [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0				0
Regulated Operating Revenue			0				0
Electric operating revenues	(1,052)		(1,032)		(2,202)		(2,100)
Natural gas operating revenues	(28)		(22)		(106)		(87)
Revenues from alternative revenue programs	(7)		8		12		38
Revenue from Related Parties	3		12		7		23
Revenues	1,076		1,074		2,327		2,248
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 operating revenues			(1,040)				(2,138)
Natural gas operating revenues			(22)				(87)
Revenue from Related Parties			12				23
Revenues			1,074				2,248
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 operating revenues			(8)				(38)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			8				38
Revenue from Related Parties			0				0
Revenues			0				0
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 operating revenues	(531)		(508)		(1,067)		(1,022)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(10)		5		10		20
Revenue from Related Parties	2		1		3		3
Revenues	523		514		1,080		1,045
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 operating revenues			(513)				(1,042)
Natural gas operating revenues			0				0
Revenue from Related Parties			1				3
Revenues			514				1,045
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 operating revenues			(5)				(20)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			5				20
Revenue from Related Parties			0				0
Revenues			0				0
Delmarva Power and Light Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0				0
Regulated Operating Revenue			0				0
Electric operating revenues	(255)		(258)		(558)		(544)
Natural gas operating revenues	(28)		(22)		(106)		(87)
Revenues from alternative revenue programs	4		0		5		9
Revenue from Related Parties	2		2		4		4
Revenues	289		282		673		644
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				0
Regulated Operating Revenue			0				0
Electric operating revenues			(258)				(553)
Natural gas operating revenues			(22)				(87)
Revenue from Related Parties			2				4
Revenues			282				644
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				0
Regulated Operating Revenue			0				0
Electric operating revenues			0				(9)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			0				9
Revenue from Related Parties			0				0
Revenues			0				0
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 operating revenues	(265)		(266)		(576)		(534)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(1)		3		(3)		9
Revenue from Related Parties	1		1		2		1
Revenues	$ 265		270		$ 575		544
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 operating revenues			(269)				(543)
Natural gas operating revenues			0				0
Revenue from Related Parties			1				1
Revenues			270				544
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 operating revenues			(3)				(9)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			3				9
Revenue from Related Parties			0				0
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.