Pension and Other Postretirement Benefits - Additional Information (Detail)		12 Months Ended
	Jul. 01, 2013	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($) Amendments	Dec. 31, 2012 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		$ 2,300,000,000	$ 2,400,000,000
Service periods for participating employee		11 years	11 years
Unfunded capital commitments		$ 9,000,000	$ 11,000,000
Pension contribution				$ 120,000,000
Percentage of participants vested		100.00%
Defined contribution plan matching contributions		$ 14,000,000	13,000,000	12,000,000
Pension and other postretirement net periodic benefit cost		97,000,000	58,000,000	95,000,000
Other postretirement benefit obligations		215,000,000	265,000,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net loss to be amortized from AOCL or regulatory assets into net periodic benefit cost		63,000,000
Prior service cost to be amortized from AOCL or regulatory assets into net periodic benefit cost		$ 7,000,000
Percentage of plan asset target allocation		68.00%
Pension and other postretirement net periodic benefit cost		$ 93,000,000	59,000,000	77,000,000
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net loss to be amortized from AOCL or regulatory assets into net periodic benefit cost		1,000,000
Prior service cost to be amortized from AOCL or regulatory assets into net periodic benefit cost		13,000,000
OPEB contributions		2,000,000	1,000,000
Pension and other postretirement net periodic benefit cost		4,000,000	(1,000,000)	18,000,000
Other postretirement benefit obligations		215,000,000	265,000,000
Potomac Electric Power Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contribution		0	0	0
Pension and other postretirement net periodic benefit cost		30,000,000	22,000,000	$ 34,000,000
Prepaid pension expense		291,000,000	316,000,000
Other postretirement benefit obligations		49,000,000	57,000,000
Potomac Electric Power Co [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of amendments, PHI approved | Amendments				2
Reduction in net periodic benefit cost			$ 7,000,000
Percentage of postretirement benefit costs			40.00%
OPEB contributions		2,000,000	$ 1,000,000	$ 6,000,000
Delmarva Power & Light Co/De [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contribution		0	0	10,000,000
Pension and other postretirement net periodic benefit cost		15,000,000	7,000,000	$ 18,000,000
Prepaid pension expense		205,000,000	220,000,000
Other postretirement benefit obligations		19,000,000	21,000,000
Delmarva Power & Light Co/De [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of amendments, PHI approved | Amendments				2
Reduction in net periodic benefit cost			4,000,000
OPEB contributions		0	0	$ 3,000,000
Delmarva Power & Light Co/De [Member] | Retiree [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contribution		0	0
PHI Service Company [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of amendments, PHI approved | Amendments				2
Reduction in net periodic benefit cost				$ 193,000,000	$ 69,000,000
Prior service credit included in projected benefit obligation				$ 124,000,000
Amortization period				10 years
Change in the discount rate	4.95%				4.10%
Reduction of the projected benefit obligation			$ 19,000,000
Percentage of postretirement benefit costs			36.00%
PHI Service Company [Member] | Retiree [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contribution		0	$ 0
Atlantic City Electric Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contribution		0	0	$ 30,000,000
Pension and other postretirement net periodic benefit cost		15,000,000	13,000,000	$ 17,000,000
Prepaid pension expense		83,000,000	96,000,000
Other postretirement benefit obligations		33,000,000	36,000,000
Atlantic City Electric Co [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of amendments, PHI approved | Amendments				2
Reduction in net periodic benefit cost			$ 3,000,000
Percentage of postretirement benefit costs			45.00%
OPEB contributions		3,000,000	$ 3,000,000	$ 6,000,000
Atlantic City Electric Co [Member] | Retiree [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contribution		0	0
Subsidiaries [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and other postretirement net periodic benefit cost		37,000,000	16,000,000	$ 26,000,000
Subsidiaries [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
OPEB contributions		$ 0	$ 0