Income Taxes - Additional Information (Detail) - USD ($)		3 Months Ended									12 Months Ended
	Feb. 26, 2015	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Income Tax [Line Items]
Tax expense (benefit)		$ 23,000,000	$ 49,000,000	$ 27,000,000	$ 30,000,000	$ 13,000,000	$ 34,000,000	$ 45,000,000	$ 46,000,000		$ 129,000,000	$ 138,000,000	$ 319,000,000
Change in estimates and interest related to uncertain tax positions													56,000,000
Establishment of valuation allowances on deferred tax assets		63,000,000				61,000,000					$ 63,000,000	61,000,000	101,000,000
PCI future deferred tax asset													101,000,000
Federal and state net operating losses, years											20 years
Federal and state net operating losses, expiration start period											2029
Federal and state net operating losses, expiration end period											2034
Unrecognized tax benefits that would impact effective tax rate		22,000,000									$ 22,000,000
Uncertain tax position pre-tax interest income (expense) recognized											35,000,000	1,000,000	(125,000,000)
Uncertain tax position after-tax interest income (expense) recognized											21,000,000		(75,000,000)
Accrued interest payable		49,000,000				47,000,000					49,000,000	47,000,000
Reduction in deferred tax liabilities		2,000,000			23,000,000
Other taxes for continuing operations											421,000,000	407,000,000	422,000,000
Uncertain tax positions settled in Global Tax Settlement											628,000,000		6,000,000
After-tax effect of revised lease rerun										$ 377,000,000
Valuation allowance for deferred tax assets													101,000,000
Change in estimates and interest related to uncertain and effectively settled tax positions											(46,000,000)		56,000,000
District of Columbia [Member]
Schedule of Income Tax [Line Items]
Corporate tax rate	9.975%
District of Columbia [Member] | 2019 [Member]
Schedule of Income Tax [Line Items]
Corporate tax rate	8.25%
District of Columbia [Member] | 2015 [Member]
Schedule of Income Tax [Line Items]
Corporate tax rate	9.40%
District of Columbia [Member] | 2016 [Member]
Schedule of Income Tax [Line Items]
Corporate tax rate	9.20%
Potomac Electric Power Co [Member]
Schedule of Income Tax [Line Items]
Tax expense (benefit)		36,000,000	32,000,000	18,000,000	12,000,000	10,000,000	38,000,000	28,000,000	16,000,000		$ 98,000,000	92,000,000	79,000,000
Federal and state net operating losses, years											20 years
Federal and state net operating losses, expiration start period											2029
Federal and state net operating losses, expiration end period											2034
Unrecognized tax benefits that would impact effective tax rate		8,000,000									$ 8,000,000
Uncertain tax position pre-tax interest income (expense) recognized											5,000,000	2,000,000	5,000,000
Uncertain tax position after-tax interest income (expense) recognized											3,000,000	1,000,000	3,000,000
Accrued interest receivable		0				9,000,000					0	9,000,000	9,000,000
Accrued interest payable		22,000,000				19,000,000					22,000,000	19,000,000
Reduction in deferred tax liabilities		2,000,000			23,000,000
Uncertain tax positions settled in Global Tax Settlement											40,000,000
Interest expense on uncertain tax positions		3,000,000
After-tax effect of revised lease rerun										377,000,000
After-tax non-cash charge										54,000,000
Additional interest income										5,000,000
Valuation allowance for deferred tax assets											0	0
Change in estimates and interest related to uncertain and effectively settled tax positions											(6,000,000)	(1,000,000)	(3,000,000)
Potomac Electric Power Co [Member] | District of Columbia [Member]
Schedule of Income Tax [Line Items]
Corporate tax rate	9.975%
Potomac Electric Power Co [Member] | District of Columbia [Member] | 2019 [Member]
Schedule of Income Tax [Line Items]
Corporate tax rate	8.25%
Potomac Electric Power Co [Member] | District of Columbia [Member] | 2015 [Member]
Schedule of Income Tax [Line Items]
Corporate tax rate	9.40%
Potomac Electric Power Co [Member] | District of Columbia [Member] | 2016 [Member]
Schedule of Income Tax [Line Items]
Corporate tax rate	9.20%
Delmarva Power & Light Co/De [Member]
Schedule of Income Tax [Line Items]
Tax expense (benefit)		14,000,000	9,000,000	5,000,000	21,000,000	14,000,000	13,000,000	13,000,000	25,000,000		$ 49,000,000	65,000,000	56,000,000
Federal and state net operating losses, years											20 years
Federal and state net operating losses, expiration start period											2029
Federal and state net operating losses, expiration end period											2034
Unrecognized tax benefits that would impact effective tax rate		3,000,000									$ 3,000,000
Uncertain tax position pre-tax interest income (expense) recognized											1,000,000	1,000,000	1,000,000
Accrued interest receivable		0				2,000,000					0	2,000,000	2,000,000
Accrued interest payable		7,000,000				7,000,000					7,000,000	7,000,000
Uncertain tax positions settled in Global Tax Settlement											9,000,000
After-tax effect of revised lease rerun										377,000,000
After-tax non-cash charge										54,000,000
Additional interest income										1,000,000
Valuation allowance for deferred tax assets											0	0
Change in estimates and interest related to uncertain and effectively settled tax positions											3,000,000		(1,000,000)
Atlantic City Electric Co [Member]
Schedule of Income Tax [Line Items]
Tax expense (benefit)		15,000,000	$ 7,000,000	$ 7,000,000	$ 2,000,000	4,000,000	$ 14,000,000	$ 4,000,000	$ 6,000,000		$ 31,000,000	28,000,000	19,000,000
Federal and state net operating losses, years											20 years
Federal and state net operating losses, expiration start period											2029
Federal and state net operating losses, expiration end period											2032
Unrecognized tax benefits that would impact effective tax rate		0									$ 0
Uncertain tax position pre-tax interest income (expense) recognized											1,000,000	1,000,000	12,000,000
Uncertain tax position after-tax interest income (expense) recognized											1,000,000	1,000,000	7,000,000
Accrued interest receivable		0				14,000,000					0	14,000,000	14,000,000
Accrued interest payable		13,000,000				13,000,000					13,000,000	13,000,000
Uncertain tax positions settled in Global Tax Settlement											3,000,000		6,000,000
After-tax effect of revised lease rerun										377,000,000
After-tax non-cash charge										54,000,000
Additional interest income										$ 6,000,000
Valuation allowance for deferred tax assets											0	0
Change in estimates and interest related to uncertain and effectively settled tax positions											3,000,000	(1,000,000)	(9,000,000)
Tax Settlement [Member]
Schedule of Income Tax [Line Items]
Total income tax benefit		(56,000,000)
Tax expense (benefit)		(47,000,000)
Income tax benefit discontinued operations		(9,000,000)
After-tax interest benefit		(21,000,000)
Uncertain tax positions settled in Global Tax Settlement		(26,000,000)
Deferred tax basis adjustments		7,000,000
Tax Settlement [Member] | Potomac Electric Power Co [Member]
Schedule of Income Tax [Line Items]
Tax expense (benefit)		(9,000,000)
After-tax interest benefit		(21,000,000)
Deferred tax basis adjustments		6,000,000
Uncertain tax positions, after-tax interest benefit		3,000,000
Uncertain tax positions settled in Global Tax Settlement		6,000,000
Tax Settlement [Member] | Delmarva Power & Light Co/De [Member]
Schedule of Income Tax [Line Items]
Tax expense (benefit)		3,000,000									3,000,000
After-tax interest benefit		(21,000,000)
Change in estimates and interest related to uncertain and effectively settled tax positions		3,000,000
Uncertain tax positions, after-tax interest benefit		1,000,000
Tax Settlement [Member] | Atlantic City Electric Co [Member]
Schedule of Income Tax [Line Items]
Tax expense (benefit)		3,000,000
After-tax interest benefit		(21,000,000)
Deferred tax basis adjustments		2,000,000
Change in estimates and interest related to uncertain and effectively settled tax positions		3,000,000
Uncertain tax positions, after-tax interest expense		1,000,000
Interest and Penalties [Member]
Schedule of Income Tax [Line Items]
Accrued interest receivable						$ 2,000,000						2,000,000	$ 2,000,000
Accrued interest payable		2,000,000									2,000,000
Pepco Energy Services' Energy Savings Performance Contract [Member]
Schedule of Income Tax [Line Items]
Tax benefit related to certain energy efficiency tax deductions											6,000,000	$ 5,000,000
Minimum [Member]
Schedule of Income Tax [Line Items]
Estimated possible decrease in unrecognized tax benefit		6,000,000									6,000,000
Minimum [Member] | Potomac Electric Power Co [Member]
Schedule of Income Tax [Line Items]
Estimated possible decrease in unrecognized tax benefit		3,000,000									3,000,000
Minimum [Member] | Delmarva Power & Light Co/De [Member]
Schedule of Income Tax [Line Items]
Estimated possible decrease in unrecognized tax benefit		0									0
Minimum [Member] | Atlantic City Electric Co [Member]
Schedule of Income Tax [Line Items]
Estimated possible decrease in unrecognized tax benefit		0									0
Maximum [Member]
Schedule of Income Tax [Line Items]
Estimated possible decrease in unrecognized tax benefit		10,000,000									10,000,000
Maximum [Member] | Potomac Electric Power Co [Member]
Schedule of Income Tax [Line Items]
Estimated possible decrease in unrecognized tax benefit		5,000,000									5,000,000
Maximum [Member] | Delmarva Power & Light Co/De [Member]
Schedule of Income Tax [Line Items]
Estimated possible decrease in unrecognized tax benefit		0									0
Maximum [Member] | Atlantic City Electric Co [Member]
Schedule of Income Tax [Line Items]
Estimated possible decrease in unrecognized tax benefit		$ 0									$ 0