Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Original Cost	$ 16,218	$ 15,465
Accumulated Depreciation	4,914	4,959
Net Book Value	11,304	10,506
Potomac Electric Power Co [Member]
Property, Plant and Equipment [Line Items]
Original Cost	8,091	7,764
Accumulated Depreciation	2,799	2,816
Net Book Value	5,292	4,948
Delmarva Power & Light Co/De [Member]
Property, Plant and Equipment [Line Items]
Original Cost	4,209	3,946
Accumulated Depreciation	1,046	1,021
Net Book Value	3,163	2,925
Atlantic City Electric Co [Member]
Property, Plant and Equipment [Line Items]
Original Cost	3,305	3,073
Accumulated Depreciation	764	760
Net Book Value	2,541	2,313
Generation [Member]
Property, Plant and Equipment [Line Items]
Original Cost	23	104
Accumulated Depreciation	19	100
Net Book Value	4	4
Generation [Member] | Atlantic City Electric Co [Member]
Property, Plant and Equipment [Line Items]
Original Cost		10
Accumulated Depreciation		9
Net Book Value		1
Distribution [Member]
Property, Plant and Equipment [Line Items]
Original Cost	10,051	9,527
Accumulated Depreciation	3,161	3,021
Net Book Value	6,890	6,506
Distribution [Member] | Potomac Electric Power Co [Member]
Property, Plant and Equipment [Line Items]
Original Cost	5,996	5,668
Accumulated Depreciation	2,199	2,082
Net Book Value	3,797	3,586
Distribution [Member] | Delmarva Power & Light Co/De [Member]
Property, Plant and Equipment [Line Items]
Original Cost	2,043	1,928
Accumulated Depreciation	490	489
Net Book Value	1,553	1,439
Distribution [Member] | Atlantic City Electric Co [Member]
Property, Plant and Equipment [Line Items]
Original Cost	2,012	1,931
Accumulated Depreciation	472	450
Net Book Value	1,540	1,481
Transmission [Member]
Property, Plant and Equipment [Line Items]
Original Cost	3,554	3,252
Accumulated Depreciation	962	934
Net Book Value	2,592	2,318
Transmission [Member] | Potomac Electric Power Co [Member]
Property, Plant and Equipment [Line Items]
Original Cost	1,378	1,306
Accumulated Depreciation	475	463
Net Book Value	903	843
Transmission [Member] | Delmarva Power & Light Co/De [Member]
Property, Plant and Equipment [Line Items]
Original Cost	1,208	1,107
Accumulated Depreciation	259	248
Net Book Value	949	859
Transmission [Member] | Atlantic City Electric Co [Member]
Property, Plant and Equipment [Line Items]
Original Cost	968	839
Accumulated Depreciation	228	223
Net Book Value	740	616
Construction Work in Progress [Member]
Property, Plant and Equipment [Line Items]
Original Cost	604	688
Net Book Value	604	688
Construction Work in Progress [Member] | Potomac Electric Power Co [Member]
Property, Plant and Equipment [Line Items]
Original Cost	318	312
Net Book Value	318	312
Construction Work in Progress [Member] | Delmarva Power & Light Co/De [Member]
Property, Plant and Equipment [Line Items]
Original Cost	107	125
Net Book Value	107	125
Construction Work in Progress [Member] | Atlantic City Electric Co [Member]
Property, Plant and Equipment [Line Items]
Original Cost	158	115
Net Book Value	158	115
Non-Operating and Other Property [Member]
Property, Plant and Equipment [Line Items]
Original Cost	1,440	1,383
Accumulated Depreciation	609	751
Net Book Value	831	632
Non-Operating and Other Property [Member] | Potomac Electric Power Co [Member]
Property, Plant and Equipment [Line Items]
Original Cost	399	478
Accumulated Depreciation	125	271
Net Book Value	274	207
Non-Operating and Other Property [Member] | Delmarva Power & Light Co/De [Member]
Property, Plant and Equipment [Line Items]
Original Cost	305	275
Accumulated Depreciation	134	131
Net Book Value	171	144
Non-Operating and Other Property [Member] | Atlantic City Electric Co [Member]
Property, Plant and Equipment [Line Items]
Original Cost	167	178
Accumulated Depreciation	64	78
Net Book Value	103	100
Gas [Member]
Property, Plant and Equipment [Line Items]
Original Cost	546	511
Accumulated Depreciation	163	153
Net Book Value	383	358
Gas [Member] | Delmarva Power & Light Co/De [Member]
Property, Plant and Equipment [Line Items]
Original Cost	546	511
Accumulated Depreciation	163	153
Net Book Value	$ 383	$ 358