Supplemental Financial Information - Summary of Other Income (Expense) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended	12 Months Ended
		Mar. 23, 2016		Dec. 31, 2016	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014		Jun. 30, 2016
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]				$ 237		$ 232		$ 216
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]				126		156		159
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units					216		(282)		180
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement					194		(197)		134
Net unrealized income (losses) on pledged assets					(1)		7		29
Regulatory offset to decommissioning trust fund-related activities	[2]				(372)		21		(358)
Total decommissioning-related activities					400		(63)		360
Investment income (loss)					17		8		1
Long-term lease income					4		15		24
Interest income related to uncertain income tax positions					13		1		40
Income Tax Examination, Penalties and Interest Expense					(106)
AFUDC—Equity					64		24		21
Terminated interest rate swaps(d)					(3)	[3]	(26)
Payments of Debt Restructuring Costs							(22)
Gain (Loss) on Disposition of Assets					(48)		18		437
Other					24		17		9
Other, net					413		(46)		455
Reclassification out of Accumulated Other Comprehensive Income [Member]
Supplemental Financial Information Tables [Line Items]
Gain (Loss) on Sale of Derivatives					26
Senior Notes [Member]
Supplemental Financial Information Tables [Line Items]
Debt Instrument, Face Amount											$ 4,200
Predecessor [Member]
Supplemental Financial Information Tables [Line Items]
Gain (Loss) on Disposition of Assets		$ 0							0
Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]				237		232		216
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]				126		156		159
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units					216		(282)		180
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement					194		(197)		134
Net unrealized income (losses) on pledged assets					(1)		7		29
Regulatory offset to decommissioning trust fund-related activities	[2]				(372)		21		(358)
Total decommissioning-related activities					400		(63)		360
Investment income (loss)					8		3		1
Long-term lease income					0		0		0
Interest income related to uncertain income tax positions					0		1		54
AFUDC—Equity					0		0		0
Terminated interest rate swaps(d)					2		0
Payments of Debt Restructuring Costs							0
Gain (Loss) on Disposition of Assets					(59)		12		437
Other					(5)		(1)		(9)
Other, net					401		(60)		406
Exelon Generation Co L L C [Member] | Senior Notes [Member]
Supplemental Financial Information Tables [Line Items]
Debt Instrument, Face Amount				$ 750	750
Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]				0		0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]				0		0		0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units					0		0		0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement					0		0		0
Net unrealized income (losses) on pledged assets					0		0		0
Regulatory offset to decommissioning trust fund-related activities	[2]				0		0		0
Total decommissioning-related activities					0		0		0
Investment income (loss)					0		0		0
Long-term lease income					0		0		0
Interest income related to uncertain income tax positions					0		0		0
Income Tax Examination, Penalties and Interest Expense					(86)
AFUDC—Equity					14		5		3
Terminated interest rate swaps(d)					0		0
Payments of Debt Restructuring Costs							0
Other					7		16		14
Other, net					(65)		21		17
PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]				0		0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]				0		0		0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units					0		0		0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement					0		0		0
Net unrealized income (losses) on pledged assets					0		0		0
Regulatory offset to decommissioning trust fund-related activities	[2]				0		0
Total decommissioning-related activities					0		0		0
Investment income (loss)					(1)		(2)		(1)
Long-term lease income					0		0		0
Interest income related to uncertain income tax positions					0		0		0
AFUDC—Equity					8		5		6
Terminated interest rate swaps(d)					0		0
Payments of Debt Restructuring Costs							0
Other					1		2		2
Other, net					8		5		7
Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]				0		0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]				0		0		0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units					0		0		0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement					0		0		0
Net unrealized income (losses) on pledged assets					0		0		0
Regulatory offset to decommissioning trust fund-related activities	[2]				0		0		0
Total decommissioning-related activities					0		0		0
Investment income (loss)					2	[4]	4		7
Long-term lease income					0		0		0
Interest income related to uncertain income tax positions					0		0		0
AFUDC—Equity					19		14		12
Terminated interest rate swaps(d)					0		0
Payments of Debt Restructuring Costs							0
Other					0		0		(1)
Other, net					21		18		18
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]			0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]			0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units				0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement				0
Net unrealized income (losses) on pledged assets				0
Regulatory offset to decommissioning trust fund-related activities	[2]			0
Total decommissioning-related activities				0
Investment income (loss)				1
Long-term lease income				0
Interest income related to uncertain income tax positions				(1)
AFUDC—Equity				23
Gain (Loss) on Disposition of Assets				(1)
Other				21
Other, net				$ 44
Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	0					0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units		0	[1]				0		0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0					0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0					0		0
Net unrealized income (losses) on pledged assets		0					0	[2]	0
Regulatory offset to decommissioning trust fund-related activities		0	[2]				0		0	[2]
Total decommissioning-related activities		0					0		0
Investment income (loss)		0					0		1
Long-term lease income		0					0		0
Interest income related to uncertain income tax positions		0					34		0
AFUDC—Equity		7					14		13
Terminated interest rate swaps(d)		0					0
Payments of Debt Restructuring Costs							0
Gain (Loss) on Disposition of Assets							46
Other		(11)					40		30
Other, net		$ (4)					88		44
Potomac Electric Power Company [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]				0		0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units					0	[1]	0		0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units					0		0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement					0		0		0
Net unrealized income (losses) on pledged assets					0		0	[2]
Regulatory offset to decommissioning trust fund-related activities					0	[2]	0		0	[2]
Total decommissioning-related activities					0		0		0
Investment income (loss)					1		0		0
Long-term lease income					0		0		0
Interest income related to uncertain income tax positions					1		5		1
AFUDC—Equity					19		12		10
Terminated interest rate swaps(d)					0		0
Payments of Debt Restructuring Costs							0
Gain (Loss) on Disposition of Assets					8		46		0
Other					15		11		19
Other, net					36		28		30
Delmarva Power and Light Company [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]				0		0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units					0	[1]	0		0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units					0		0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement					0		0		0
Net unrealized income (losses) on pledged assets					0		0	[2]
Regulatory offset to decommissioning trust fund-related activities					0	[2]	0		0	[2]
Total decommissioning-related activities					0		0		0
Investment income (loss)					0		0		0
Long-term lease income					0		0		0
Interest income related to uncertain income tax positions					0		0		0
AFUDC—Equity					5		1		2
Terminated interest rate swaps(d)					0		0
Payments of Debt Restructuring Costs							0
Other					8		9		8
Other, net					13		10		10
Atlantic City Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]				0		0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units					0	[1]	0		0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units					0		0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement					0		0		0
Net unrealized income (losses) on pledged assets					0		0	[2]
Regulatory offset to decommissioning trust fund-related activities					0	[2]	0		0	[2]
Total decommissioning-related activities					0		0		0
Investment income (loss)					1		0	[4]	0	[4]
Long-term lease income					0		0		0
Interest income related to uncertain income tax positions					0		0		1
AFUDC—Equity					6		1		1
Terminated interest rate swaps(d)					0		0
Payments of Debt Restructuring Costs							0
Other					2		2		1
Other, net					$ 9		$ 3		$ 3

[1] Includes investment income and realized gains and losses on sales of investments within the nuclear decommissioning 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 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 are probable not to occur. As a result, $26 million of anticipated payments were reclassified from AOCI to Other, net in Exelon's Consolidated Statements of Operations and Comprehensive Income.

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