Supplemental Financial Information - Operations (Detail) - USD ($) $ in Millions			3 Months Ended					6 Months Ended
		Mar. 31, 2016	Jun. 30, 2016	Jun. 30, 2016	Mar. 23, 2016	Jun. 30, 2015		Jun. 30, 2016	Jun. 30, 2015
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			$ 217			$ 132		$ 369	$ 279
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units			90			93	[1]	122	164	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units			39			74	[1]	61	104	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units			52			(133)		131	(85)
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement			48			(96)		100	(56)
Net unrealized income (losses) on pledged assets			1					3	9
Regulatory offset to decommissioning trust fund-related activities			(117)			28	[2]	(211)	(78)	[2]
Total decommissioning-related activities			113			(34)		206	58
Investment income			(6)			(1)		(12)	(4)
Long-term lease income						(4)		(4)	(8)
Unrecognized Tax Benefits Interest Income			4					5	0
AFUDC - equity			(15)			(5)		(24)	(11)
Gain (Loss) on Disposition of Assets	[3]								(26)
Gains (Losses) on Extinguishment of Debt								(3)
Other Income			6			7		10	9
Other, net			144			(17)		258	64
Exelon Generation Co L L C [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			27			24		55	51
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units			90			93	[1]	122	164	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units			39			74	[1]	61	104	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units			52			(133)		131	(85)
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement			48			(96)		100	(56)
Net unrealized income (losses) on pledged assets			1					3	9
Regulatory offset to decommissioning trust fund-related activities			(117)			28	[2]	(211)	(78)	[2]
Total decommissioning-related activities			113			(34)		206	58
Investment income			(5)			0		(5)	(1)
Unrecognized Tax Benefits Interest Income			0					0	1
Gain (Loss) on Disposition of Assets									0
Gains (Losses) on Extinguishment of Debt								(2)
Other Income			(1)			3		1	2
Other, net			117			(31)		210	62
Commonwealth Edison Co [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			60			55		119	117
Decommissioning-Related Activities [Abstract]
Investment income			0
Unrecognized Tax Benefits Interest Income								0	0
AFUDC - equity			(1)			(1)		(3)	(1)
Other Income			2			4		4	8
Other, net			3			5		7	9
PECO Energy Co [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			32			32		66	67
Decommissioning-Related Activities [Abstract]
Investment income			0			1		1	1
Unrecognized Tax Benefits Interest Income			0					0	0
AFUDC - equity			(2)			(1)		(4)	(3)
Other Income			0			1		1	1
Other, net			2			1		4	3
Baltimore Gas and Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			21			21		45	44
Decommissioning-Related Activities [Abstract]
Investment income			0			(1)	[4]	(2)	(2)	[4]
Unrecognized Tax Benefits Interest Income			0					0
AFUDC - equity			(5)			(3)		(9)	(7)
Other Income			0			0		0	(1)
Other, net			5			4		11	8
Potomac Electric Power Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			73			77		152	157
Decommissioning-Related Activities [Abstract]
Investment income			0			0		0	0
Long-term lease income						0		0	0
Unrecognized Tax Benefits Interest Income			0					1	0
AFUDC - equity			(5)			(3)		(9)	(6)
Gain (Loss) on Disposition of Assets			8					8
Other Income			1			5		4	7
Other, net			6			8		14	13
Pepco Holdings LLC [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		$ 84	77		$ 77	81			166
Pepco Holdings LLC [Member] | Successor [Member]
Decommissioning-Related Activities [Abstract]
Investment income		0
Long-term lease income		0
Unrecognized Tax Benefits Interest Income		0
AFUDC - equity		(8)	(7)
Other Income		4	4
Other, net		$ 12	11	$ 12
Pepco Holdings LLC [Member] | Predecessor [Member]
Decommissioning-Related Activities [Abstract]
Investment income					0				0
Long-term lease income					0				0
Unrecognized Tax Benefits Interest Income					0				0
AFUDC - equity					(7)	(3)			(7)
Other Income					(11)	9			14
Other, net					$ (4)	12			21
Delmarva Power and Light Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			4			4		9	9
Decommissioning-Related Activities [Abstract]
Investment income			0			0		0	0
Long-term lease income						0		0	0
Unrecognized Tax Benefits Interest Income			0					0	0
AFUDC - equity			(1)			0		(2)	0
Other Income			2			2		4	5
Other, net			3			2		6	5
Atlantic City Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes			0			0		0	0
Decommissioning-Related Activities [Abstract]
Investment income			0			0		0	0
Long-term lease income						0		0	0
Unrecognized Tax Benefits Interest Income			0					1	0
AFUDC - equity			(1)			0		(3)	(1)
Gain (Loss) on Disposition of Assets			1					1
Other Income			1			1		1	2
Other, net			$ 2			$ 1		$ 5	$ 3

[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 2015 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

[3] In January 2015, in connection with Generation's $750 million issuance of five-year Senior Unsecured Notes, Exelon terminated certain floating-to-fixed interest rate swaps. As the original forecasted transactions were a series of future interest payments over a ten year period, a portion of the anticipated interest payments were probable not to occur. As a result, $26 million of anticipated payments were reclassified from AOCI to Other, net in Exelon's Consolidated Statement of Operations and Comprehensive Income.

[4] Relates to the cash return on BGE’s rate stabilization deferral. See Note 3 — Regulatory Matters of the Exelon 2015 Form 10-K for additional information regarding the rate stabilization deferral.