Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Original Cost	$ 15,465	$ 14,567
Accumulated Depreciation	4,959	4,863
Net Book Value	10,506	9,704
Generation [Member]
Property, Plant and Equipment [Line Items]
Original Cost	104	105
Accumulated Depreciation	100	99
Net Book Value	4	6
Distribution [Member]
Property, Plant and Equipment [Line Items]
Original Cost	9,527	8,896
Accumulated Depreciation	3,021	2,961
Net Book Value	6,506	5,935
Transmission [Member]
Property, Plant and Equipment [Line Items]
Original Cost	3,252	2,991
Accumulated Depreciation	934	908
Net Book Value	2,318	2,083
Gas [Member]
Property, Plant and Equipment [Line Items]
Original Cost	511	481
Accumulated Depreciation	153	142
Net Book Value	358	339
Construction Work in Progress [Member]
Property, Plant and Equipment [Line Items]
Original Cost	688	677
Net Book Value	688	677
Non-Operating and Other Property [Member]
Property, Plant and Equipment [Line Items]
Original Cost	1,383	1,417
Accumulated Depreciation	751	753
Net Book Value	632	664
Potomac Electric Power Co [Member]
Property, Plant and Equipment [Line Items]
Original Cost	7,764	7,310
Accumulated Depreciation	2,816	2,772
Net Book Value	4,948	4,538
Potomac Electric Power Co [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Original Cost	5,668	5,287
Accumulated Depreciation	2,082	2,027
Net Book Value	3,586	3,260
Potomac Electric Power Co [Member] | Transmission [Member]
Property, Plant and Equipment [Line Items]
Original Cost	1,306	1,223
Accumulated Depreciation	463	444
Net Book Value	843	779
Potomac Electric Power Co [Member] | Construction Work in Progress [Member]
Property, Plant and Equipment [Line Items]
Original Cost	312	312
Net Book Value	312	312
Potomac Electric Power Co [Member] | Non-Operating and Other Property [Member]
Property, Plant and Equipment [Line Items]
Original Cost	478	488
Accumulated Depreciation	271	301
Net Book Value	207	187
Delmarva Power & Light Co/De [Member]
Property, Plant and Equipment [Line Items]
Original Cost	3,946	3,673
Accumulated Depreciation	1,021	1,016
Net Book Value	2,925	2,657
Delmarva Power & Light Co/De [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Original Cost	1,928	1,788
Accumulated Depreciation	489	492
Net Book Value	1,439	1,296
Delmarva Power & Light Co/De [Member] | Transmission [Member]
Property, Plant and Equipment [Line Items]
Original Cost	1,107	982
Accumulated Depreciation	248	243
Net Book Value	859	739
Delmarva Power & Light Co/De [Member] | Gas [Member]
Property, Plant and Equipment [Line Items]
Original Cost	511	481
Accumulated Depreciation	153	142
Net Book Value	358	339
Delmarva Power & Light Co/De [Member] | Construction Work in Progress [Member]
Property, Plant and Equipment [Line Items]
Original Cost	125	158
Net Book Value	125	158
Delmarva Power & Light Co/De [Member] | Non-Operating and Other Property [Member]
Property, Plant and Equipment [Line Items]
Original Cost	275	264
Accumulated Depreciation	131	139
Net Book Value	144	125
Atlantic City Electric Co [Member]
Property, Plant and Equipment [Line Items]
Original Cost	3,073	2,901
Accumulated Depreciation	760	751
Net Book Value	2,313	2,150
Atlantic City Electric Co [Member] | Generation [Member]
Property, Plant and Equipment [Line Items]
Original Cost	10	10
Accumulated Depreciation	9	9
Net Book Value	1	1
Atlantic City Electric Co [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Original Cost	1,931	1,821
Accumulated Depreciation	450	442
Net Book Value	1,481	1,379
Atlantic City Electric Co [Member] | Transmission [Member]
Property, Plant and Equipment [Line Items]
Original Cost	839	786
Accumulated Depreciation	223	221
Net Book Value	616	565
Atlantic City Electric Co [Member] | Construction Work in Progress [Member]
Property, Plant and Equipment [Line Items]
Original Cost	115	110
Net Book Value	115	110
Atlantic City Electric Co [Member] | Non-Operating and Other Property [Member]
Property, Plant and Equipment [Line Items]
Original Cost	178	174
Accumulated Depreciation	78	79
Net Book Value	$ 100	$ 95