Changes in Accumulated Other Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2016		Sep. 30, 2015		Sep. 30, 2016		Sep. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues		$ 9,002		$ 7,401		$ 23,486		$ 22,746
Income before income taxes		871		703		1,597		2,767
Income taxes		(340)		(115)		(625)		(805)
Net income		526		587		956		1,959
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		562		619		1,052		2,047
Other, net		120		(244)		377		(179)
Equity in (losses) earnings of unconsolidated affiliates						(15)		(3)
Interest Expense		506		243		1,148		724
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	[1]	(5)				(5)
Income taxes	[1]	0				0
Net income	[1]	(5)		(46)		(5)		(152)
Other, net		(5)				(5)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	[1]			(4)		5		(35)
Income taxes	[1]			1		(2)		13
Net income	[1]			(3)		3		(22)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues	[1]							2
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	[1]					2		10
Interest Expense						5		(11)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest Rate Swap [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other, net	[1]							(26)
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	[1]	(57)		(71)		(170)		(213)
Income taxes		22	[1]	28	[1]	66	[1]	83
Net income	[1]	(35)		(43)		(104)		(130)
Prior service benefit reclassified to periodic benefit cost		19		19		57		57
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax	[1],[2]	(76)		(90)		(227)		(270)
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	[1]					(106)
Exelon Generation Co L L C [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues		5,035		4,768		13,363		14,841
Income before income taxes		450		297		865		1,583
Income taxes		(173)		36		(293)		(371)
Net income		271		332		556		1,208
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		275		319		558		1,184
Other, net		185		(257)		395		(193)
Equity in (losses) earnings of unconsolidated affiliates						(16)		(4)
Interest Expense		67		56		243		236
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	[1]	(5)				(5)
Income taxes	[1]	0				0
Net income	[1]	(5)		(3)		(5)		(6)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	[1]	(5)
Other, net		(5)				(5)
Exelon Generation Co L L C [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	[1]			(4)		5		(9)
Income taxes				1	[1]	(2)	[1]	(3)
Net income	[1]			(3)		3		(6)
Exelon Generation Co L L C [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues	[1]							2
Exelon Generation Co L L C [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense						5		(11)
Exelon Generation Co L L C [Member] | Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	[1]					(2)
PEPCO Holdings Inc [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income				(1)				(5)
PEPCO Holdings Inc [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues								0
Income before income taxes				(1)		0		(1)
Income taxes				0		0		0
Net income				(1)		0		(1)
PEPCO Holdings Inc [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues						0
Interest Expense				(1)				(1)
PEPCO Holdings Inc [Member] | Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes				(2)		(1)		(7)
Income taxes				(2)		0		3
Net income				0		(1)		(4)
Prior service benefit reclassified to periodic benefit cost				0		0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax				(2)		(1)		(7)
Potomac Electric Power Company [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues		635		592		1,695		1,641
Income before income taxes		114		92		54		190
Income taxes		(35)		(32)		(34)		(62)
Net income		79		60		20		128
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		79		60		20		128
Other, net		12		8		28		21
Equity in (losses) earnings of unconsolidated affiliates						0		0
Interest Expense		30		31		98		92
Delmarva Power and Light Company [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues		331		314		974		1,004
Income before income taxes		63		24		2		89
Income taxes		(19)		(9)		(18)		(34)
Net income		44		15		(16)		55
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		44		15		(16)		55
Other, net		3		4		9		8
Equity in (losses) earnings of unconsolidated affiliates						0		0
Interest Expense		12		12		37		37
Atlantic City Electric Company [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues		421		386		982		1,003
Income before income taxes		70		36		(58)		60
Income taxes		(23)		(14)		8		(23)
Net income		47		22		(50)		37
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		47		22		(50)		37
Other, net		2		1		8		4
Equity in (losses) earnings of unconsolidated affiliates						0		0
Interest Expense		$ 15		16		$ 47		$ 48
Interest Expense [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense				(4)
Interest Expense [Member] | Exelon Generation Co L L C [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense				$ (4)

[1] Amounts in parenthesis represent a decrease in net income.

[2] This AOCI component is included in the computation of net periodic pension and OPEB cost (see Note 13 — Retirement Benefits for additional details).