Supplemental Financial Information - Operations (Detail) - USD ($) $ in Millions			3 Months Ended
		Mar. 31, 2016	Mar. 31, 2016	Mar. 23, 2016	Mar. 31, 2015		Dec. 31, 2015
Supplemental Income Statement Information [Line Items]
Utility Taxes			$ 153		$ 148
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units			34		71	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units			21		29	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units			79		48
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement			52		40
Net unrealized income (losses) on pledged assets			2		10
Regulatory offset to decommissioning trust fund-related activities			(95)		(106)	[2]
Total decommissioning-related activities			93		92
Investment income			6		1
Long-term lease income			4		4
Unrecognized Tax Benefits Interest Income			1		0
AFUDC - equity			8		5
Gain (Loss) on Disposition of Assets	[3]				(23)
Gain (Loss) on Sale of Derivatives					26
Other Income			4		1
Other, net			114		80
Capitalized Costs, Asset Retirement Costs		$ 62	62				$ 56
Gains (Losses) on Extinguishment of Debt			(2)
Exelon Generation Co L L C [Member]
Supplemental Income Statement Information [Line Items]
Utility Taxes			28		27
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units			34		71	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units			21		29	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units			79		48
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement			52		40
Net unrealized income (losses) on pledged assets			2		10
Regulatory offset to decommissioning trust fund-related activities			(95)		(106)	[2]
Total decommissioning-related activities			93		92
Investment income			1		1
Unrecognized Tax Benefits Interest Income			0		1
Gain (Loss) on Disposition of Assets					3
Other Income			1		(3)
Other, net			93		94
Capitalized Costs, Asset Retirement Costs		62	62				56
Gains (Losses) on Extinguishment of Debt			(2)
Commonwealth Edison Co [Member]
Supplemental Income Statement Information [Line Items]
Utility Taxes			59		62
Decommissioning-Related Activities [Abstract]
AFUDC - equity			2
Other Income			2		3
Other, net			4		3
Capitalized Costs, Asset Retirement Costs		0	0				0
PECO Energy Co [Member]
Supplemental Income Statement Information [Line Items]
Utility Taxes			35		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
Capitalized Costs, Asset Retirement Costs		0	0
Baltimore Gas and Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utility Taxes			24		24
Decommissioning-Related Activities [Abstract]
Investment income			1		1	[4]
Unrecognized Tax Benefits Interest Income			0
AFUDC - equity			3		3
Other Income			0		0
Other, net			4		4
Capitalized Costs, Asset Retirement Costs		0	0				0
Potomac Electric Power Company [Member]
Supplemental Income Statement Information [Line Items]
Utility Taxes			79		80
Decommissioning-Related Activities [Abstract]
Investment income			0		0
Long-term lease income			0		0
Unrecognized Tax Benefits Interest Income			1		0
AFUDC - equity			4		3
Other Income			4		2
Other, net			9		5
Capitalized Costs, Asset Retirement Costs							0
PEPCO Holdings Inc [Member]
Supplemental Income Statement Information [Line Items]
Utility Taxes		7		$ 77	85
PEPCO Holdings Inc [Member] | Successor [Member]
Decommissioning-Related Activities [Abstract]
Investment income		0
Long-term lease income		0
Unrecognized Tax Benefits Interest Income		0
AFUDC - equity		1
Other Income		1
Other, net		2
PEPCO Holdings Inc [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	4
Other Income				(11)	5
Other, net				$ (4)	9
Capitalized Costs, Asset Retirement Costs							0
Delmarva Power and Light Company [Member]
Supplemental Income Statement Information [Line Items]
Utility Taxes			5		5
Decommissioning-Related Activities [Abstract]
Investment income			0		0
Long-term lease income			0		0
Unrecognized Tax Benefits Interest Income			0		0
AFUDC - equity			1		0
Other Income			2		2
Other, net			3		2
Capitalized Costs, Asset Retirement Costs		4	4				0
Atlantic City Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utility Taxes			0		0
Decommissioning-Related Activities [Abstract]
Investment income			0		0
Long-term lease income			0		0
Unrecognized Tax Benefits Interest Income			1		0
AFUDC - equity			2		1
Other Income			1		0
Other, net			4		$ 1
Capitalized Costs, Asset Retirement Costs		$ 2	$ 2				$ 0

[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.