Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	$ 1,078	$ 1,829	$ 2,175
Increases based on tax positions related to current year	108	108	15
Unrecognized Tax Benefits, Increase Resulting from Acquisition	22
Unrecognized Tax Benefits, Period Increase (Decrease)	(332)	(705)	(255)
Increases based on tax positions prior to current year	88	79	18
Decreases based on tax positions prior to current year	(21)	(116)	(1)
Decrease from settlements with taxing authorities	(27)	(31)	(35)
Unrecognized tax benefits - ending balance	916	1,078	1,829
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0	(86)	(88)
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	534	1,357	1,415
Increases based on tax positions related to current year	10	0	15
Unrecognized Tax Benefits, Increase Resulting from Acquisition	5
Unrecognized Tax Benefits, Period Increase (Decrease)	(12)	(659)	33
Increases based on tax positions prior to current year	0	65	18
Decreases based on tax positions prior to current year	(20)	(112)	(2)
Decrease from settlements with taxing authorities	(27)	(31)	(34)
Unrecognized tax benefits - ending balance	490	534	1,357
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0	(86)	(88)
Commonwealth Edison Co [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	142	149	324
Increases based on tax positions related to current year	0	0	0
Unrecognized Tax Benefits, Period Increase (Decrease)	(154)	(7)	(175)
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	0
Unrecognized tax benefits - ending balance	(12)	142	149
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0	0	0
PECO Energy Co [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	0	44	44
Increases based on tax positions related to current year	0	0	0
Unrecognized Tax Benefits, Period Increase (Decrease)	0	(44)	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	0
Unrecognized tax benefits - ending balance	0	0	44
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0	0	0
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	120	0	0
Increases based on tax positions related to current year	0	106	0
Unrecognized Tax Benefits, Period Increase (Decrease)	0	0	0
Increases based on tax positions prior to current year	0	14	0
Decreases based on tax positions prior to current year	0	0	0
Decrease from settlements with taxing authorities	0	0	0
Unrecognized tax benefits - ending balance	120	120	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0	0	0
Potomac Electric Power Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	8	0	45
Increases based on tax positions related to current year	21	0	0
Unrecognized Tax Benefits, Period Increase (Decrease)	0	0	(45)
Increases based on tax positions prior to current year	51	8	0
Decreases based on tax positions prior to current year	0	0	0
Decrease from settlements with taxing authorities	0	0	0
Unrecognized tax benefits - ending balance	80	8	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0	0	0
Delmarva Power and Light Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	3	0	3
Increases based on tax positions related to current year	16	0	0
Unrecognized Tax Benefits, Period Increase (Decrease)	0	0	(3)
Increases based on tax positions prior to current year	18	3	0
Decreases based on tax positions prior to current year	0	0	0
Decrease from settlements with taxing authorities	0	0	0
Unrecognized tax benefits - ending balance	37	3	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0	0	0
Atlantic City Electric Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	0	0	3
Increases based on tax positions related to current year	22	0	0
Unrecognized Tax Benefits, Period Increase (Decrease)	0	0	(3)
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	0
Unrecognized tax benefits - ending balance	22	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0	0	0
Pepco Holdings LLC [Member] | Successor [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	22
Increases based on tax positions related to current year	59
Unrecognized Tax Benefits, Increase Resulting from Acquisition	(5)
Unrecognized Tax Benefits, Period Increase (Decrease)	0
Increases based on tax positions prior to current year	96
Decreases based on tax positions prior to current year	0
Decrease from settlements with taxing authorities	0
Unrecognized tax benefits - ending balance	172	22
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0
Pepco Holdings LLC [Member] | Predecessor [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	$ 22	702	743
Increases based on tax positions related to current year		0	0
Unrecognized Tax Benefits, Period Increase (Decrease)		(688)	(41)
Increases based on tax positions prior to current year		11	0
Decreases based on tax positions prior to current year		0	0
Decrease from settlements with taxing authorities		0	0
Unrecognized tax benefits - ending balance		22	702
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		$ (3)	$ 0