Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	$ 1,829	$ 2,175	$ 1,024
Increases based on tax positions related to current year	108	15	19
Changes to tax positions that only affect timing	(705)	(255)	649
Increases based on tax positions prior to current year	79	18	493
Decreases based on tax positions prior to current year	(116)	(1)	(6)
Decrease from settlements with taxing authorities	(31)	(35)
Decreases from expiration of statute of limitations	(86)	(88)	(4)
Unrecognized tax benefits - ending balance	1,078	1,829	2,175
Exelon Generation Co L L C [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	1,357	1,415	876
Increases based on tax positions related to current year	0	15	19
Changes to tax positions that only affect timing	(659)	33	36
Increases based on tax positions prior to current year	65	18	493
Decreases based on tax positions prior to current year	(112)	(2)	(5)
Decrease from settlements with taxing authorities	(31)	(34)
Decreases from expiration of statute of limitations	(86)	(88)	(4)
Unrecognized tax benefits - ending balance	534	1,357	1,415
Commonwealth Edison Co [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	149	324	67
Increases based on tax positions related to current year	0	0	0
Changes to tax positions that only affect timing	(7)	(175)	257
Increases based on tax positions prior to current year	0	0	0
Decreases based on tax positions prior to current year	0	0	0
Decrease from settlements with taxing authorities	0	0
Decreases from expiration of statute of limitations	0	0	0
Unrecognized tax benefits - ending balance	142	149	324
PECO Energy Co [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	44	44	44
Increases based on tax positions related to current year	0	0	0
Changes to tax positions that only affect timing	(44)	0	0
Increases based on tax positions prior to current year	0	0	0
Decreases based on tax positions prior to current year	0	0	0
Decrease from settlements with taxing authorities	0	0
Decreases from expiration of statute of limitations	0	0	0
Unrecognized tax benefits - ending balance	0	44	44
Baltimore Gas and Electric Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	0	0	0
Increases based on tax positions related to current year	106	0	0
Changes to tax positions that only affect timing	0	0	0
Increases based on tax positions prior to current year	14	0	0
Decreases based on tax positions prior to current year	0	0	0
Decrease from settlements with taxing authorities	0	0
Decreases from expiration of statute of limitations	0	0	0
Unrecognized tax benefits - ending balance	$ 120	$ 0	$ 0