Changes in Accumulated Other Comprehensive Income - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended										12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Mar. 23, 2016		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues		$ 7,875	$ 9,002	$ 6,910	$ 7,573			$ 6,702	$ 7,401	$ 6,514	$ 8,830	$ 31,360		$ 29,447		$ 27,429
Interest expense												(1,123)		(1,079)		(610)
Other Nonoperating Income (Expense)												413		(46)		455
Income before income taxes												1,989		3,330		2,486
Income tax benefit (expense)												(761)		(1,073)		(666)
Net income												1,204		2,250		1,820
Net Income (Loss) Available to Common Stockholders, Basic		204	490	267	173			309	629	638	693	1,134		2,269		1,623
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]											(150)		(196)	[2],[3]
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax												(8)		(21)	[2],[3]
Accumulated Defined Benefit Plans Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax												(137)		(175)	[1],[2],[3]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]											(224)		(287)
Reclassification from AOCI, Current Period, Tax	[1]											(87)		(112)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1],[4]											78		74
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]											(302)	[4]	(361)	[5]
Accumulated Translation Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax												(5)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income before income taxes	[1]											(13)		(35)
Income tax benefit (expense)	[1]											5		14
Net income	[1]											(8)		(21)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	[1]													2
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense	[1]											(13)		(11)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] | Interest Rate Swap [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense	[1]													(26)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Translation Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	[1]											(5)
Interest expense	[1]					$ 0						0
Income tax benefit (expense)	[1]											0
Net income	[1]											(5)
Exelon Generation Co L L C [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues		$ 4,388	$ 5,035	$ 3,589	$ 4,739			4,294	4,768	4,232	5,840	17,751		19,135		17,393
Interest expense												37		(425)		50
Other Nonoperating Income (Expense)												401		(60)		406
Income tax benefit (expense)												(290)		(502)		(207)
Net income												558		1,340		1,019
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]											(13)		(5)	[2],[3]
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 on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax												(8)		(5)	[2],[3]
Exelon Generation Co L L C [Member] | Accumulated Translation Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax												(5)
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income before income taxes	[1]											(13)		(9)
Income tax benefit (expense)												5	[1]	(4)
Net income	[1]											(8)		(5)
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	[1]													2
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense												(13)	[1]	(11)
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Translation Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	[1]											(5)
Income before income taxes	[1]											(5)
Income tax benefit (expense)	[1]											0
Net income	[1]											(5)
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]
Net income	[1]											$ (137)
Predecessor [Member] | Pepco Holdings LLC [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues						1,153		$ 1,126	$ 1,336	$ 1,119	$ 1,354			4,935		4,808
Interest expense						(69)								(192)		(225)
Other Nonoperating Income (Expense)						(4)								88		44
Income tax benefit (expense)						(17)								(163)		(138)
Net income						19								327		$ 242
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]					(1)								(5)	[2],[3]
Predecessor [Member] | Pepco Holdings LLC [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]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[2]													(1)
Predecessor [Member] | Pepco Holdings LLC [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax						(1)								(4)	[1],[2],[3]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]					(1)								(6)
Reclassification from AOCI, Current Period, Tax	[1]					0								(2)
Predecessor [Member] | Pepco Holdings LLC [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1],[4]					0								0
Predecessor [Member] | Pepco Holdings LLC [Member] | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1],[4]					(1)								(6)
Predecessor [Member] | Pepco Holdings LLC [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income before income taxes	[1]					0								(1)
Income tax benefit (expense)	[1]					0								0
Net income	[1]					0								(1)
Predecessor [Member] | Pepco Holdings LLC [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] | Energy Related Derivative [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	[1]													0
Predecessor [Member] | Pepco Holdings LLC [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense						0	[1]							$ (1)
Predecessor [Member] | Pepco Holdings LLC [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Translation Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	[1]					0
Interest expense	[1]					0
Income before income taxes	[1]					0
Income tax benefit (expense)	[1]					0
Net income	[1]					0
Predecessor [Member] | Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [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]
Net income	[1]					$ (1)

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

[2] All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.

[3] See next tables for details about these reclassifications.

[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.