Changes in Accumulated Other Comprehensive Income - Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	[1]	$ (2,596)	$ (2,673)	$ (2,624)	$ (2,684)
Pension and non-pension postretirement benefit plans:
Prior service benefit reclassified to periodic benefit cost		7	8
Actuarial loss reclassified to periodic cost		(30)	(35)
Pension and non-pension postretirement benefit plans valuation adjustment		0	17
Change in unrealized gain/(loss) on cash flow hedges		3	(2)
Change in unrealized loss on equity investments		2	0
Change in unrealized loss on marketable securities		1	0
Total		(17)	(12)
OCI before reclassifications	[1]	59	(49)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1],[2]	31	(60)
Other Comprehensive Income (Loss), Net of Tax	[1]	28	11
PEPCO Holdings Inc [Member] | Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net		(35)	(45)	(36)	(46)
Pension and non-pension postretirement benefit plans:
OCI before reclassifications		2	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(1)	1
Other Comprehensive Income (Loss), Net of Tax		1	1
Exelon Generation Co L L C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	[1]	(64)	(53)	(63)	(36)
Pension and non-pension postretirement benefit plans:
Change in unrealized gain/(loss) on cash flow hedges		2	5
Change in unrealized loss on equity investments		2	0
Total		4	5
OCI before reclassifications	[1]	(4)	(18)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1],[2]	(3)	(1)
Other Comprehensive Income (Loss), Net of Tax	[1]	(1)	(17)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	[1]	(26)	(22)
Pension and non-pension postretirement benefit plans:
OCI before reclassifications	[1]		(11)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1],[2]	(3)	(17)
Other Comprehensive Income (Loss), Net of Tax	[1]	(7)	6
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]
Accumulated other comprehensive loss, net		(8)	(9)	(8)	(9)
Pension and non-pension postretirement benefit plans:
OCI before reclassifications		0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		0	0
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]
Accumulated other comprehensive loss, net	[1]	(26)	(23)
Pension and non-pension postretirement benefit plans:
OCI before reclassifications	[1]		(6)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1],[2]	(3)	(1)
Other Comprehensive Income (Loss), Net of Tax	[1]	(5)	(5)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	[1]	2	3	3
Pension and non-pension postretirement benefit plans:
OCI before reclassifications	[1]	(1)	0
Other Comprehensive Income (Loss), Net of Tax	[1]	(1)	0
Accumulated Net Unrealized Investment Gain (Loss) [Member] | PEPCO Holdings Inc [Member] | Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net		0	0	0	0
Pension and non-pension postretirement benefit plans:
OCI before reclassifications			0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		0
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]
Accumulated other comprehensive loss, net	[1]	1	1		1
Pension and non-pension postretirement benefit plans:
OCI before reclassifications	[1]	0	0
Other Comprehensive Income (Loss), Net of Tax	[1]	0	0
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	[1]	(2,532)	(2,623)	(2,565)	(2,640)
Pension and non-pension postretirement benefit plans:
OCI before reclassifications	[1]	67
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1],[2]	34	(43)
Other Comprehensive Income (Loss), Net of Tax	[1]	33	17
Accumulated Defined Benefit Plans Adjustment [Member] | PEPCO Holdings Inc [Member] | Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net		(27)	(36)		(37)
Pension and non-pension postretirement benefit plans:
OCI before reclassifications		2	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(1)	1
Other Comprehensive Income (Loss), Net of Tax		1	1
Accumulated Defined Benefit Plans Adjustment [Member] | Exelon Generation Co L L C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	[1]		0		0
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	[1]	(34)	(31)	(40)
Pension and non-pension postretirement benefit plans:
OCI before reclassifications	[1]	6	(12)
Other Comprehensive Income (Loss), Net of Tax	[1]	6	(12)
Accumulated Translation Adjustment [Member] | PEPCO Holdings Inc [Member] | Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net		0	0	0	0
Pension and non-pension postretirement benefit plans:
OCI before reclassifications		0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			0
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]
Accumulated other comprehensive loss, net	[1]	(34)	(31)	(40)
Pension and non-pension postretirement benefit plans:
OCI before reclassifications	[1]	6	(12)
Other Comprehensive Income (Loss), Net of Tax	[1]	6	(12)
Accumulated Equity Investment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	[1]	(6)	0	(3)	0
Pension and non-pension postretirement benefit plans:
OCI before reclassifications	[1]	(3)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1],[2]	0	0
Other Comprehensive Income (Loss), Net of Tax	[1]	(3)	0
Accumulated Equity Investment [Member] | PEPCO Holdings Inc [Member] | Predecessor [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net		0	0	0	0
Pension and non-pension postretirement benefit plans:
OCI before reclassifications		0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		0	0
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]
Accumulated other comprehensive loss, net	[1]	(5)	0	$ (3)	$ 0
Pension and non-pension postretirement benefit plans:
OCI before reclassifications	[1]	(2)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1],[2]	0	0
Other Comprehensive Income (Loss), Net of Tax	[1]	$ (2)	$ 0

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

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