Changes in Accumulated Other Comprehensive Income - Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016		Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]			$ (7)		$ (48)
Pension and non-pension postretirement benefit plans:
Prior service benefit reclassified to periodic benefit cost		$ 7	$ 8	15		15
Actuarial loss reclassified to periodic cost		(30)	(35)	(60)		(69)
Pension and non-pension postretirement benefit plans valuation adjustment		0	0	1		17
Change in unrealized gain/(loss) on cash flow hedges		2	(2)	4		(6)
Change in unrealized loss on equity investments		1	0	3		0
Change in unrealized gain on marketable securities		(1)	1	0		1
Total		(21)	(28)	(37)		(42)
Other Comprehensive Income (Loss), Net of Tax		31	50	59	[1]	58	[1]
PEPCO Holdings Inc [Member]
Pension and non-pension postretirement benefit plans:
Actuarial loss reclassified to periodic cost			0			1
PEPCO Holdings Inc [Member] | Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax				0		0
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax				1		4
Exelon Generation Co L L C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]			1		(14)
Pension and non-pension postretirement benefit plans:
Change in unrealized gain/(loss) on cash flow hedges		1	(1)	3		1
Change in unrealized loss on equity investments		1	0	3		0
Change in unrealized gain on marketable securities		0	0	0		1
Total		2	(1)	6		2
Other Comprehensive Income (Loss), Net of Tax		$ 0	$ 6	(2)	[1]	(11)	[1]
PECO Energy Co [Member]
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax	[1]					0
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]					(10)
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax	[1]			(7)		9
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | PEPCO Holdings Inc [Member] | Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax				0		0
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax				0		0
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Exelon Generation Co L L C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]					(6)
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax	[1]			(4)		(3)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | PECO Energy Co [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]					0
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]			0		0
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax	[1]			0		0
Accumulated Net Unrealized Investment Gain (Loss) [Member] | PEPCO Holdings Inc [Member] | Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax				0		0
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax				0		0
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Exelon Generation Co L L C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]			0		1
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax	[1]			0		1
Accumulated Net Unrealized Investment Gain (Loss) [Member] | PECO Energy Co [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]					0
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax				(2)	[1]	(29)
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax	[1]			67		58
Accumulated Defined Benefit Plans Adjustment [Member] | PEPCO Holdings Inc [Member] | Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax				0		0
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax				1		4
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]			6		(9)
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax	[1]			6		(9)
Accumulated Translation Adjustment [Member] | PEPCO Holdings Inc [Member] | Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax				0		0
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax				0		0
Accumulated Translation Adjustment [Member] | Exelon Generation Co L L C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]			6		(9)
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax	[1]			6		(9)
Accumulated Translation Adjustment [Member] | PECO Energy Co [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]					0
Accumulated Equity Investment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]			(7)		0
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax	[1]			(7)		0
Accumulated Equity Investment [Member] | PEPCO Holdings Inc [Member] | Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax				0		0
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax				0		0
Accumulated Equity Investment [Member] | Exelon Generation Co L L C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]			(4)		0
Pension and non-pension postretirement benefit plans:
Other Comprehensive Income (Loss), Net of Tax	[1]			$ (4)		0
Accumulated Equity Investment [Member] | PECO Energy Co [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]					$ 0

[1] All amounts are net of tax. Amounts in parenthesis represent a decrease in AOCI.