Income Taxes - Reconciliation of Consolidated Income Tax Expense from Continuing Operations (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate									$ 156,000,000	$ 133,000,000	$ 150,000,000
State income taxes, net of federal effect									27,000,000	23,000,000	27,000,000
Asset removal costs									(14,000,000)	(12,000,000)	(14,000,000)
Change in estimates and interest related to uncertain and effectively settled tax positions									(46,000,000)		56,000,000
Deferred tax basis adjustments									7,000,000
Establishment of valuation allowances related to deferred tax assets											101,000,000
Merger related costs									4,000,000	7,000,000
Other, net									(5,000,000)	(13,000,000)	(1,000,000)
Consolidated Income Tax Expense Related to Continuing Operations	$ 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
Income tax at Federal statutory rate, percentage									35.00%	35.00%	35.00%
State income taxes, net of federal effect, percentage									6.00%	6.10%	6.30%
Asset removal costs, percentage									(3.10%)	(3.20%)	(3.30%)
Change in estimates and interest related to uncertain and effectively settled tax positions, percentage									(10.30%)		13.10%
Deferred tax basis adjustments, percentage									1.60%
Establishment of valuation allowances related to deferred tax assets, percentage											23.50%
Merger related costs, percentage									0.90%	1.80%
Other, net, percentage									(1.20%)	(3.40%)	(0.20%)
Consolidated income tax expense related to continuing operations, percentage									28.90%	36.30%	74.40%
Potomac Electric Power Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate									$ 100,000,000	$ 92,000,000	$ 80,000,000
State income taxes, net of federal effect									15,000,000	15,000,000	13,000,000
Asset removal costs									(14,000,000)	(12,000,000)	(14,000,000)
Change in estimates and interest related to uncertain and effectively settled tax positions									(6,000,000)	(1,000,000)	(3,000,000)
Deferred tax basis adjustments									6,000,000
Establishment of valuation allowances related to deferred tax assets									0	0
Other, net									(3,000,000)	(2,000,000)	3,000,000
Consolidated Income Tax Expense Related to Continuing Operations	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
Income tax at Federal statutory rate, percentage									35.00%	35.00%	35.00%
State income taxes, net of federal effect, percentage									5.30%	5.70%	5.70%
Asset removal costs, percentage									(4.90%)	(4.60%)	(6.10%)
Change in estimates and interest related to uncertain and effectively settled tax positions, percentage									(2.10%)	(0.40%)	(1.30%)
Deferred tax basis adjustments, percentage									2.10%
Other, net, percentage									(1.00%)	(0.70%)	1.20%
Consolidated income tax expense related to continuing operations, percentage									34.40%	35.00%	34.50%
Delmarva Power & Light Co/De [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate									$ 44,000,000	$ 59,000,000	$ 51,000,000
State income taxes, net of federal effect									7,000,000	9,000,000	8,000,000
Change in estimates and interest related to uncertain and effectively settled tax positions									3,000,000		(1,000,000)
Establishment of valuation allowances related to deferred tax assets									0	0
Other, net									(5,000,000)	(3,000,000)	(2,000,000)
Consolidated Income Tax Expense Related to Continuing Operations	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
Income tax at Federal statutory rate, percentage									35.00%	35.00%	35.00%
State income taxes, net of federal effect, percentage									5.60%	5.30%	5.50%
Change in estimates and interest related to uncertain and effectively settled tax positions, percentage									2.40%		(0.70%)
Other, net, percentage									(3.80%)	(1.80%)	(1.20%)
Consolidated income tax expense related to continuing operations, percentage									39.20%	38.50%	38.60%
Atlantic City Electric Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate									$ 24,000,000	$ 26,000,000	$ 24,000,000
State income taxes, net of federal effect									4,000,000	4,000,000	5,000,000
Change in estimates and interest related to uncertain and effectively settled tax positions									3,000,000	(1,000,000)	(9,000,000)
Deferred tax basis adjustments									2,000,000		(2,000,000)
Establishment of valuation allowances related to deferred tax assets									0	0
Investment tax credit amortization											(1,000,000)
Other, net									(2,000,000)	(1,000,000)	2,000,000
Consolidated Income Tax Expense Related to Continuing Operations	$ 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
Income tax at Federal statutory rate, percentage									35.00%	35.00%	35.00%
State income taxes, net of federal effect, percentage									5.80%	5.50%	7.20%
Change in estimates and interest related to uncertain and effectively settled tax positions, percentage									4.30%	(1.40%)	(13.00%)
Deferred tax basis adjustments, percentage									2.90%		(2.90%)
Investment tax credit amortization, percentage											(1.40%)
Other, net, percentage									(3.10%)	(0.70%)	2.60%
Consolidated income tax expense related to continuing operations, percentage									44.90%	38.40%	27.50%