Supplemental Financial Information - Operations (Detail) - USD ($) $ in Millions			3 Months Ended
		Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016		Mar. 23, 2016
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			$ 224	$ 153
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units			68	34	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units			32	21	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units			222	79
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement			166	52
Net unrealized income (losses) on pledged assets			(1)	2
Regulatory offset to decommissioning trust fund-related activities			(234)	(95)	[2]
Total decommissioning-related activities			253	93
Investment income			2	6
Long-term lease income				4
Unrecognized Tax Benefits Interest Income			1	1
AFUDC - equity			17	8
Gains (Losses) on Extinguishment of Debt	[3]			(2)
Other Income			10	4
Other, net			283	114
Exelon Generation Co L L C [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			32	28
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]		68	34
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]		32	21
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units			222	79
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement			166	52
Net unrealized income (losses) on pledged assets			(1)	2
Regulatory offset to decommissioning trust fund-related activities	[2]		(234)	(95)
Total decommissioning-related activities			253	93
Investment income			2	1
Unrecognized Tax Benefits Interest Income			0	0
Gains (Losses) on Extinguishment of Debt				(2)
Other Income			4	1
Other, net			259	93
Commonwealth Edison Co [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			59	59
Decommissioning-Related Activities [Abstract]
Investment income			0
Unrecognized Tax Benefits Interest Income			0	0
AFUDC - equity			2	2
Other Income			2	2
Other, net			4	4
PECO Energy Co [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			31	35
Decommissioning-Related Activities [Abstract]
Investment income			0	0
Unrecognized Tax Benefits Interest Income			0	0
AFUDC - equity			2	2
Other Income			0	0
Other, net			2	2
Baltimore Gas and Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			26	24
Decommissioning-Related Activities [Abstract]
Investment income			0	1	[4]
Unrecognized Tax Benefits Interest Income			0
AFUDC - equity			4	3
Other Income			0	0
Other, net			4	4
Potomac Electric Power Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			71	79
Decommissioning-Related Activities [Abstract]
Investment income			0	0
Long-term lease income				0
Unrecognized Tax Benefits Interest Income			0	1
AFUDC - equity			5	4
Other Income			3	4
Other, net			8	9
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		$ 7	76
Decommissioning-Related Activities [Abstract]
Investment income		0	0
Long-term lease income		0
Unrecognized Tax Benefits Interest Income		0	0
AFUDC - equity		1	9
Other Income		1	4
Other, net		$ 2	13
Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes						$ 77
Decommissioning-Related Activities [Abstract]
Investment income						0
Long-term lease income						0
Unrecognized Tax Benefits Interest Income						0
AFUDC - equity						7
Other Income						(11)
Other, net						$ (4)
Delmarva Power and Light Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			5	5
Decommissioning-Related Activities [Abstract]
Investment income			0	0
Long-term lease income				0
Unrecognized Tax Benefits Interest Income			0	0
AFUDC - equity			2	1
Other Income			1	2
Other, net			3	3
Atlantic City Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			0	0
Decommissioning-Related Activities [Abstract]
Investment income			0	0
Long-term lease income				0
Unrecognized Tax Benefits Interest Income			0	1
AFUDC - equity			2	2
Other Income			0	1
Other, net			$ 2	$ 4

[1] Includes investment income and realized gains and losses on sales of investments of the trust funds.

[2] Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 16 — Asset Retirement Obligations of the Exelon 2016 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

[3] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOjk4YjY2MmVjNTk5ZDQ4ZGNhYWRkOTNkYjIyYTc3MzFkfFRleHRTZWxlY3Rpb246OEU0NzY4ODA4OERBNTYzQUFFQjI2MDMyNzhGRDg2RUUM}

[4] .