Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	$ (2,684)		$ (2,040)
OCI before reclassifications		(136)		(528)	[1]
Amounts reclassified from AOCI		196		(116)	[1],[2]
Other comprehensive income (loss)		60		(644)	[1]	$ 727
Ending balance		(2,624)		(2,684)	[1]	(2,040)	[1]
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	(28)		120
OCI before reclassifications		(12)		(31)	[1]
Amounts reclassified from AOCI		21		(117)	[1],[2]
Other comprehensive income (loss)		9		(148)	[1]
Ending balance		(19)		(28)	[1]	120	[1]
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		3	[1]	2
OCI before reclassifications		0		(1)
Amounts reclassified from AOCI		0		2
Other comprehensive income (loss)		0		1	[1]
Ending balance		3		3	[1]	2
Accumulated Defined Benefit Plans Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		(2,640)	[1]	(2,260)
OCI before reclassifications		(100)		(498)	[1]
Amounts reclassified from AOCI		175		118	[1],[2]
Other comprehensive income (loss)		75		(380)	[1]
Ending balance		(2,565)		(2,640)	[1]	(2,260)
Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		(19)	[1]	(10)
OCI before reclassifications		(21)		(9)
Other comprehensive income (loss)		(21)		(9)	[1]
Ending balance		(40)		(19)	[1]	(10)
Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	0		108
OCI before reclassifications		(3)		11	[1]
Amounts reclassified from AOCI		0		(119)	[1],[2]
Other comprehensive income (loss)		(3)		(108)	[1]
Ending balance		(3)		0	[1]	108	[1]
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	(36)		214
OCI before reclassifications		(32)		(14)	[1]
Amounts reclassified from AOCI		5		(236)	[1],[2]
Other comprehensive income (loss)		(27)		(250)	[1]	(299)
Ending balance		(63)		(36)	[1]	214	[1]
Exelon Generation Co L L C [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	(18)		114
OCI before reclassifications		(8)		(15)	[1]
Amounts reclassified from AOCI		5		(117)	[1],[2]
Other comprehensive income (loss)		(3)		(132)	[1]
Ending balance		(21)		(18)	[1]	114	[1]
Exelon Generation Co L L C [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	1		2
OCI before reclassifications		0		(1)
Other comprehensive income (loss)		0		(1)	[1]
Ending balance		1		1	[1]	2	[1]
Exelon Generation Co L L C [Member] | Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		(19)	[1]	(10)
OCI before reclassifications		(21)		(9)	[1]
Other comprehensive income (loss)		(21)		(9)	[1]
Ending balance		(40)		(19)	[1]	(10)
Exelon Generation Co L L C [Member] | Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	0		108
OCI before reclassifications		(3)		11	[1]
Amounts reclassified from AOCI		0		(119)	[1],[2]
Other comprehensive income (loss)		(3)		(108)	[1]
Ending balance		(3)		0	[1]	108	[1]
PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	1		1
Ending balance		1		1	[1]	1	[1]
PECO Energy Co [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	1		1
Ending balance		$ 1		$ 1	[1]	$ 1	[1]

[1] All amounts are net of tax. Amounts in parenthesis represent a decrease in accumulated other comprehensive income.

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