Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Income Tax [Line Items]
Tax benefit related to certain energy efficiency tax deductions		$ 5,000,000
Change in estimates and interest related to uncertain tax positions			56,000,000
Establishment of valuation allowances on deferred tax assets	101,000,000		101,000,000
PCI future deferred tax asset	101,000,000		101,000,000
Income tax settlement with IRS				8,000,000
Federal and state net operating losses, years		20 years
Federal and state net operating losses, expiration period		2029 to 2034
Unrecognized tax benefits that would impact effective tax rate		12,000,000
Uncertain tax position pre-tax interest income (expense) recognize			(125,000,000)	23,000,000
Uncertain tax position after-tax interest income (expense) recognized			(75,000,000)	14,000,000
Accrued interest receivable		2,000,000	2,000,000	10,000,000
Estimated possible decrease in unrecognized tax benefit lower range		700,000,000
Estimated possible decrease in unrecognized tax benefit upper range		800,000,000
Other taxes for continuing operations		407,000,000	422,000,000	426,000,000
After-tax effect of revised lease rerun	377,000,000
Valuation allowance for deferred tax assets			101,000,000
Less Than [Member]
Schedule of Income Tax [Line Items]
Uncertain tax position pre-tax interest income (expense) recognize		(1,000,000)
Potomac Electric Power Co [Member]
Schedule of Income Tax [Line Items]
Income tax settlement with IRS				10,000,000
Federal and state net operating losses, years		20 years
Federal and state net operating losses, expiration period		2029 to 2034
Unrecognized tax benefits that would impact effective tax rate		1,000,000
Uncertain tax position pre-tax interest income (expense) recognize		2,000,000	5,000,000	18,000,000
Uncertain tax position after-tax interest income (expense) recognized		1,000,000	3,000,000	11,000,000
Accrued interest receivable		9,000,000	9,000,000	5,000,000
Estimated possible decrease in unrecognized tax benefit lower range		65,000,000
Estimated possible decrease in unrecognized tax benefit upper range		85,000,000
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
Amended state returns		20,000,000
Refunds received		4,000,000
Income tax remaining recoverable amount		16,000,000
Delmarva Power & Light Co/De [Member]
Schedule of Income Tax [Line Items]
Federal and state net operating losses, years		20 years
Federal and state net operating losses, expiration period		2029 to 2034
Unrecognized tax benefits that would impact effective tax rate		1,000,000
Uncertain tax position pre-tax interest income (expense) recognize		1,000,000	1,000,000	1,000,000
Accrued interest receivable		2,000,000	2,000,000	1,000,000
Estimated possible decrease in unrecognized tax benefit lower range		14,000,000
Estimated possible decrease in unrecognized tax benefit upper range		18,000,000
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
Atlantic City Electric Co [Member]
Schedule of Income Tax [Line Items]
Income tax settlement with IRS				1,000,000
Federal and state net operating losses, years		20 years
Federal and state net operating losses, expiration period		2029 to 2032
Unrecognized tax benefits that would impact effective tax rate		0
Uncertain tax position pre-tax interest income (expense) recognize		1,000,000	12,000,000	2,000,000
Uncertain tax position after-tax interest income (expense) recognized		1,000,000	7,000,000	1,000,000
Accrued interest receivable		14,000,000	14,000,000	7,000,000
Estimated possible decrease in unrecognized tax benefit lower range		6,000,000
Estimated possible decrease in unrecognized tax benefit upper range		8,000,000
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
Amended state returns		$ 1,000,000