Changes in Accumulated Other Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2016		Jun. 30, 2015		Jun. 30, 2016		Jun. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues		$ 6,910		$ 6,514		$ 14,485		$ 15,345
Income before income taxes		415		962		725		2,064
Income taxes		(102)		(327)		(285)		(690)
Net income		306		633		430		1,372
Other, net		144		(17)		258		64
Equity in (losses) earnings of unconsolidated affiliates						(10)		(2)
Interest Expense		366		145		643		480
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	[1]	(34)		(46)		(66)		(106)
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]			(2)		5		(29)
Income taxes	[1]			0		(2)		10
Net income	[1]			(2)		3		(19)
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
Interest Expense						5		(5)
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]	(56)		(71)		(113)		(142)
Income taxes		22	[1]	27	[1]	44	[1]	55
Net income	[1]	(34)		(44)		(69)		(87)
Prior service benefit reclassified to periodic benefit cost		19		19		38		38
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax	[1],[2]	(75)		(90)		(151)		(180)
Exelon Generation Co L L C [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues		3,589		4,232		8,329		10,074
Income before income taxes		5		573		416		1,285
Income taxes		31		(181)		(120)		(407)
Net income		28		390		285		875
Other, net		117		(31)		210		62
Equity in (losses) earnings of unconsolidated affiliates						(11)		(3)
Interest Expense		89		90		176		180
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]
Net income	[1]	0		(2)		3		(3)
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]			(2)		5		(3)
Income taxes				0	[1]	(2)	[1]	0
Net income	[1]			(2)		3		(3)
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		(5)
PEPCO Holdings Inc [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income				(3)		(1)		(4)
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				0		0		0
Income taxes				0		0		0
Net income				0		0		0
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		0		0
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				(3)		(1)		(5)
Income taxes				0		0		1
Net income				(3)		(1)		(4)
Prior service benefit reclassified to periodic benefit cost				0		0		0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax				(3)		(1)		(5)
Potomac Electric Power Company [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues		509		504		1,061		1,049
Income before income taxes		72		60		(61)		98
Income taxes		(23)		(18)		1		(30)
Net income		49		42		(60)		68
Other, net		6		8		14		13
Equity in (losses) earnings of unconsolidated affiliates						0		0
Interest Expense		31		31		68		61
Delmarva Power and Light Company [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues		281		271		643		691
Income before income taxes		20		13		(61)		66
Income taxes		(8)		(5)		1		(26)
Net income		12		8		(60)		40
Other, net		3		2		6		5
Equity in (losses) earnings of unconsolidated affiliates						0		0
Interest Expense		13		13		25		25
Atlantic City Electric Company [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues		270		285		561		618
Income before income taxes		5		10		(128)		24
Income taxes		(2)		(4)		31		(9)
Net income		3		6		(97)		15
Other, net		2		1		5		3
Equity in (losses) earnings of unconsolidated affiliates						0		0
Interest Expense		$ 16		$ 16		$ 32		$ 32

[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).