Changes in Accumulated Other Comprehensive Income - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		2 Months Ended	3 Months Ended										12 Months Ended
		Dec. 31, 2014	Dec. 31, 2015		Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014		Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues			$ 6,702		$ 7,401	$ 6,514	$ 8,830	$ 7,255	$ 6,912	$ 6,024	$ 7,237		$ 29,447		$ 27,429	$ 24,888
Interest expense													(1,079)		(610)	(896)
Prior service costs													30		19	0
Sale of equity method investment													(46)		455	460
Total income (loss) in equity method investments															(20)	10
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain (Loss), Net													0		289	0
Income before income taxes													3,330		2,486	2,773
Income tax benefit (expense)													(1,073)		(666)	(1,044)
Net income			309	[1]	629	638	693	18	993	522	90	[2]	2,250		1,820	1,729
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income	[3]												(196)		116
Reclassification out of Accumulated Other Comprehensive Income [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income	[3]														(2)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues													(26)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	[3]														(2)
Income before income taxes	[3]												(35)		195
Income tax benefit (expense)	[3]												14		(78)
Net income	[3]												(21)		117
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	[3]												2		195
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense	[3]												(11)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Equity Method Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Total income (loss) in equity method investments	[3]														5
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain (Loss), Net															193
Income before income taxes	[3]														198
Income tax benefit (expense)	[3]														(79)
Net income	[3]														119
Exelon Generation Co L L C [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues		$ 386	4,294		4,768	4,232	5,840	4,802	4,412	3,789	4,390		19,135		17,393	15,630
Interest expense													(425)		50	(2)
Sale of equity method investment													(60)		406	355
Total income (loss) in equity method investments													8		(20)	10
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain (Loss), Net													0		289	0
Income tax benefit (expense)													(502)		(207)	(615)
Net income		$ (42)	$ 154		$ 377	$ 398	$ 443	$ (91)	$ 771	$ 340	$ (185)		1,340		1,019	$ 1,060
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net income	[3]												(5)		236
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income before income taxes	[3]												(9)		195
Income tax benefit (expense)													4	[3]	78
Net income	[3]												(5)		117
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	[3]												2		195
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense	[3]												(11)
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Equity Method Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Total income (loss) in equity method investments	[3]														5
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain (Loss), Net															193
Income before income taxes	[3]														198
Income tax benefit (expense)	[3]														(79)
Net income	[3]														119
Pension Plan, Defined Benefit [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Prior service costs	[3],[4]												74		46
Actuarial gains/losses	[3],[4]												(361)
Income before income taxes	[3]												(287)		(193)
Income tax benefit (expense)	[3]												112		75
Net income	[3]												$ (175)		(118)
Pension Plan, Defined Benefit [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Equity Method Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Actuarial gains/losses	[3],[5]														$ (239)

[1] Includes charges to earnings related to the impairments of certain generating assets which were held for sale and certain Upstream exploration assets. See Note 8—Impairment of Long-Lived Assets of the Combined Notes to Consolidated Financial Statements for additional information.

[2] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmJiZTkxZGVlYTU0NDQzYzU5MmI5ODA2YTIzODFjMGRkfFRleHRTZWxlY3Rpb246NEExNTZFREE4NkYwMUZCQUZDQTExMjI1RThCRDM3QzcM}

[3] Amounts in parenthesis 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 17 — Retirement Benefits for additional details).

[5] Amortization of the deferred compensation unit plan is allocated to capital and operating and maintenance expense.