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, 2015		Sep. 30, 2014		Sep. 30, 2015		Sep. 30, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues		$ 7,401	[1]	$ 6,912	[1]	$ 22,746	[2]	$ 20,173	[2]
Income before income taxes		703		1,496		2,767		2,371
Income taxes		(115)		(422)		(805)		(646)
Net income		587		1,074		1,959		1,725
Prior service benefit reclassified to periodic benefit cost		8		8		22		11
Other Nonoperating Income (Expense)		(244)		16		(179)		346
Equity in losses of unconsolidated affiliates				0		(3)		(20)
Interest Expense		243		247		724		691
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	[3]	(46)		(7)		(152)		106
Reclassification out of Accumulated Other Comprehensive Income [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues						2
Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest Rate Swap [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues						26
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	[3]	(4)		28		(35)		130
Income taxes	[3]	1		(12)		13		(52)
Net income	[3]	(3)		16		(22)		78
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				28				130
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		4
Other Nonoperating Income (Expense)						(11)
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]	(71)		(42)		(213)		(149)
Income taxes		28	[3]	16		83	[3]	58
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	[3]	(43)				(130)
Net income	[3]			(26)				(91)
Prior service benefit reclassified to periodic benefit cost		19	[3],[4]	19		57	[3],[4]	29
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax		(90)	[3],[4]	(61)		(270)	[3],[4]	(178)
Equity Method Investments | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	[3]			5				198
Income taxes				(2)				(79)
Net income	[3]			3				119
Other Nonoperating Income (Expense)				5				5
Gain on consolidation of CENG								193
Exelon Generation Co L L C [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues		4,768		4,412		14,841		12,591
Income before income taxes		297		1,140		1,583		1,327
Income taxes		36		(291)		(371)		(290)
Net income		332		849		1,208		1,037
Other Nonoperating Income (Expense)		(257)		4		(193)		306
Equity in losses of unconsolidated affiliates				1		(4)		(20)
Interest Expense		56		77		236		224
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	[3]	(3)		19		(6)		197
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues						2
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest Rate Swap [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Revenues						0
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	[3]	(4)		28		(9)		130
Income taxes	[3]	1		(12)		3		(52)
Net income	[3]	(3)		16		(6)		78
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				28				130
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]
Revenues		4
Other Nonoperating Income (Expense)						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]
Income before income taxes		0	[3]	0		0	[3]	0
Income taxes		0	[3]	0		0	[3]	0
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	[3]	0				0
Net income				0				0
Prior service benefit reclassified to periodic benefit cost		0	[3],[4]	0		0	[3],[4]	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax		$ 0	[3],[4]	0		$ 0	[3],[4]	0
Exelon Generation Co L L C [Member] | Equity Method Investments | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	[3]			5				198
Income taxes				(2)				(79)
Net income	[3]			3				119
Other Nonoperating Income (Expense)				$ 5				5
Gain on consolidation of CENG								$ 193

[1] (c)For the three months ended September 30, 2015 and 2014, utility taxes of $28 million and $22 million, respectively, are included in revenues and expenses for Generation. For the three months ended September 30, 2015 and 2014, utility taxes of $63 million and $61 million, respectively, are included in revenues and expenses for ComEd. For the three months ended September 30, 2015 and 2014, utility taxes of $37 million and $34 million, respectively, are included in revenues and expenses for PECO. For the three months ended September 30, 2015 and 2014, utility taxes of $23 million and $21 million, respectively, are included in revenues and expenses for BGE.

[2] (d)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.

[3] All amounts are net of tax. Amounts in parentheses represent a decrease in net income.

[4] This accumulated other comprehensive income component is included in the computation of net periodic pension and OPEB cost (see Note 14— Retirement Benefits for additional details).