Debt - Components of Long-Term Debt (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Apr. 15, 2014	Jun. 30, 2014	Mar. 31, 2014
Debt Instrument [Line Items]
Debt instrument, carrying value	$ 806	$ 906
Debt instrument, carrying value	806	906
Debt instrument, carrying value	4,817	4,470
Net unamortized premium(discount)	(10)	(14)
Current portion of long-term debt	(366)	(403)
Total net long-term debt	4,441	4,053
Total long-term debt	4,817	4,470
First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	3,889	3,321
Total long-term debt	3,889	3,321
Medium-Term Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	40	40
Debt instrument, carrying value	40	40
Transition Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	215	255
Current portion of long-term debt	(44)	(41)
Total Net Long-Term Debt	171	214
Total long-term debt	215	255
4.65% Due 2014 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	4.65%		4.65%
Debt instrument maturity date	2014
Debt instrument, interest percentage	4.65%		4.65%
Debt instrument maturity date	2014
Debt instrument, carrying value		175
Total long-term debt		175
3.05% Due 2022 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	3.05%
Debt instrument maturity date	2022
Debt instrument, interest percentage	3.05%
Debt instrument maturity date	2022
Debt instrument, carrying value	200	200
Total long-term debt	200	200
6.20% Due 2022 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	6.20%
Debt instrument maturity date	2022
Debt instrument, interest percentage	6.20%
Debt instrument maturity date	2022
Debt instrument, carrying value	110	110
Total long-term debt	110	110
3.60% Due 2024 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	3.60%
Debt instrument maturity date	2024
Debt instrument, interest percentage	3.60%
Debt instrument maturity date	2024
Debt instrument, carrying value	400
Total long-term debt	400
5.75% Due 2034 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	5.75%
Debt instrument maturity date	2034
Debt instrument, interest percentage	5.75%
Debt instrument maturity date	2034
Debt instrument, carrying value	100	100
Total long-term debt	100	100
5.40% Due 2035 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	5.40%
Debt instrument maturity date	2035
Debt instrument, interest percentage	5.40%
Debt instrument maturity date	2035
Debt instrument, carrying value	175	175
Total long-term debt	175	175
6.50% Due 2037 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	6.50%
Debt instrument maturity date	2037
Debt instrument, interest percentage	6.50%
Debt instrument maturity date	2037
Debt instrument, carrying value	500	500
Total long-term debt	500	500
7.90% Due 2038 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	7.90%
Debt instrument maturity date	2038
Debt instrument, interest percentage	7.90%
Debt instrument maturity date	2038
Debt instrument, carrying value	250	250
Total long-term debt	250	250
4.15% Due 2043 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	4.15%
Debt instrument maturity date	2043
Debt instrument, interest percentage	4.15%
Debt instrument maturity date	2043
Debt instrument, carrying value	250	250
Total long-term debt	250	250
4.95% Due 2043 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	4.95%
Debt instrument maturity date	2043
Debt instrument, interest percentage	4.95%
Debt instrument maturity date	2043
Debt instrument, carrying value	150	150
Total long-term debt	150	150
3.50% Due 2023 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	3.50%
Debt instrument, interest percentage	3.50%
2.70% Due 2015 [Member] | Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	250	250
Debt interest percentage	2.70%
Debt instrument maturity date	2015
Debt instrument, interest percentage	2.70%
Debt instrument, carrying value	250	250
Debt instrument maturity date	2015
5.90% Due 2016 [Member] | Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	190	190
Debt interest percentage	5.90%
Debt instrument maturity date	2016
Debt instrument, interest percentage	5.90%
Debt instrument, carrying value	190	190
Debt instrument maturity date	2016
6.125% Due 2017 [Member] | Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	81	81
Debt interest percentage	6.125%
Debt instrument maturity date	2017
Debt instrument, interest percentage	6.125%
Debt instrument, carrying value	81	81
Debt instrument maturity date	2017
7.45% Due 2032 [Member] | Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	185	185
Debt interest percentage	7.45%
Debt instrument maturity date	2032
Debt instrument, interest percentage	7.45%
Debt instrument, carrying value	185	185
Debt instrument maturity date	2032
4.46% Due 2016 [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value		8
Total long-term debt		8
4.91% Due 2017 [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	17	46
Total long-term debt	17	46
5.05% Due 2020 [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	51	54
Total long-term debt	51	54
5.55% Due 2023 [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	147	147
Total long-term debt	147	147
Atlantic City Electric Co [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	904	861
Net unamortized premium(discount)	(1)	(1)
Current portion of long-term debt	(15)	(107)
Total net long-term debt	888	753
Total long-term debt	904	861
Atlantic City Electric Co [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	904	761
Total long-term debt	904	761
Atlantic City Electric Co [Member] | Variable Rate Term Loan [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value		100
Debt instrument maturity date	2014
Debt instrument, carrying value		100
Debt instrument maturity date	2014
Atlantic City Electric Co [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	215	255
Current portion of long-term debt	(44)	(41)
Total Net Long-Term Debt	171	214
Total long-term debt	215	255
Atlantic City Electric Co [Member] | 7.63% Due 2014 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	7.63%
Debt instrument maturity date	2014
Debt instrument, interest percentage	7.63%
Debt instrument maturity date	2014
Debt instrument, carrying value		7
Total long-term debt		7
Atlantic City Electric Co [Member] | 7.68% Due 2015 - 2016 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	7.68%
Debt instrument, interest percentage	7.68%
Debt instrument maturity date, start	2015
Debt instrument maturity date, end	2016
Debt instrument maturity date, start	2015
Debt instrument maturity date, end	2016
Debt instrument, carrying value	17	17
Total long-term debt	17	17
Atlantic City Electric Co [Member] | 7.75% Due 2018 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	7.75%
Debt instrument maturity date	2018
Debt instrument, interest percentage	7.75%
Debt instrument maturity date	2018
Debt instrument, carrying value	250	250
Total long-term debt	250	250
Atlantic City Electric Co [Member] | 6.80% Due 2021 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	6.80%
Debt instrument maturity date	2021
Debt instrument, interest percentage	6.80%
Debt instrument maturity date	2021
Debt instrument, carrying value	39	39
Total long-term debt	39	39
Atlantic City Electric Co [Member] | 4.35% Due 2021 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	4.35%
Debt instrument maturity date	2021
Debt instrument, interest percentage	4.35%
Debt instrument maturity date	2021
Debt instrument, carrying value	200	200
Total long-term debt	200	200
Atlantic City Electric Co [Member] | 3.375% Due 2024 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	3.375%
Debt instrument maturity date	2024
Debt instrument, interest percentage	3.375%
Debt instrument maturity date	2024
Debt instrument, carrying value	150
Total long-term debt	150
Atlantic City Electric Co [Member] | 4.875% Due 2029 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	4.875%
Debt instrument maturity date	2029
Debt instrument, interest percentage	4.875%
Debt instrument maturity date	2029
Debt instrument, carrying value	23	23
Total long-term debt	23	23
Atlantic City Electric Co [Member] | 5.80% Due 2034 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	5.80%
Debt instrument maturity date	2034
Debt instrument, interest percentage	5.80%
Debt instrument maturity date	2034
Debt instrument, carrying value	120	120
Total long-term debt	120	120
Atlantic City Electric Co [Member] | 5.80% Due 2036 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	5.80%
Debt instrument maturity date	2036
Debt instrument, interest percentage	5.80%
Debt instrument maturity date	2036
Debt instrument, carrying value	105	105
Total long-term debt	105	105
Atlantic City Electric Co [Member] | 4.46% Due 2016 [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	4.46%
Debt instrument maturity date	2016
Debt instrument, interest percentage	4.46%
Debt instrument maturity date	2016
Debt instrument, carrying value		8
Total long-term debt		8
Atlantic City Electric Co [Member] | 4.91% Due 2017 [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	4.91%
Debt instrument maturity date	2017
Debt instrument, interest percentage	4.91%
Debt instrument maturity date	2017
Debt instrument, carrying value	17	46
Total long-term debt	17	46
Atlantic City Electric Co [Member] | 5.05% Due 2020 [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	5.05%
Debt instrument maturity date	2020
Debt instrument, interest percentage	5.05%
Debt instrument maturity date	2020
Debt instrument, carrying value	51	54
Total long-term debt	51	54
Atlantic City Electric Co [Member] | 5.55% Due 2023 [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	5.55%
Debt instrument maturity date	2023
Debt instrument, interest percentage	5.55%
Debt instrument maturity date	2023
Debt instrument, carrying value	147	147
Total long-term debt	147	147
Delmarva Power & Light Co/De [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	1,068	968
Net unamortized premium(discount)	3	(1)
Current portion of long-term debt	(100)	(100)
Total net long-term debt	971	867
Total long-term debt	1,068	968
Delmarva Power & Light Co/De [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	850	650
Debt instrument, carrying value	850	650
Debt instrument, carrying value	78	78
Total long-term debt	78	78
Delmarva Power & Light Co/De [Member] | Unsecured Tax-Exempt Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	78	78
Debt instrument, carrying value	78	78
Delmarva Power & Light Co/De [Member] | Medium-Term Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	40	40
Debt instrument, carrying value	40	40
Delmarva Power & Light Co/De [Member] | Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	100	200
Debt instrument, carrying value	100	200
Delmarva Power & Light Co/De [Member] | 5.22% Due 2016 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	100	100
Debt interest percentage	5.22%
Debt instrument maturity date	2016
Debt instrument, interest percentage	5.22%
Debt instrument, carrying value	100	100
Debt instrument maturity date	2016
Debt instrument, carrying value	100	100
Total long-term debt	100	100
Delmarva Power & Light Co/De [Member] | 3.50% Due 2023 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	500	300
Debt interest percentage	3.50%			3.50%
Debt instrument maturity date	2023
Debt instrument, interest percentage	3.50%			3.50%
Debt instrument, carrying value	500	300
Debt instrument maturity date	2023
Debt instrument, carrying value	500	300
Total long-term debt	500	300
Delmarva Power & Light Co/De [Member] | 4.00% Due 2042 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	250	250
Debt interest percentage	4.00%
Debt instrument maturity date	2042
Debt instrument, interest percentage	4.00%
Debt instrument, carrying value	250	250
Debt instrument maturity date	2042
Debt instrument, carrying value	250	250
Total long-term debt	250	250
Delmarva Power & Light Co/De [Member] | 5.40% Due 2031 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	78	78
Total long-term debt	78	78
Delmarva Power & Light Co/De [Member] | 5.40% Due 2031 [Member] | Unsecured Tax-Exempt Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	78	78
Debt interest percentage	5.40%
Debt instrument maturity date	2031
Debt instrument, interest percentage	5.40%
Debt instrument, carrying value	78	78
Debt instrument maturity date	2031
Delmarva Power & Light Co/De [Member] | 7.56% - 7.58% Due 2017 [Member] | Medium-Term Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	14	14
Debt instrument maturity date	2017
Debt instrument, carrying value	14	14
Debt instrument maturity date	2017
Debt instrument percentage, minimum	7.56%
Debt instrument percentage, maximum	7.58%
Debt instrument percentage, minimum	7.56%
Debt instrument percentage, maximum	7.58%
Delmarva Power & Light Co/De [Member] | 6.81% Due 2018 [Member] | Medium-Term Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	4	4
Debt interest percentage	6.81%
Debt instrument maturity date	2018
Debt instrument, interest percentage	6.81%
Debt instrument, carrying value	4	4
Debt instrument maturity date	2018
Delmarva Power & Light Co/De [Member] | 7.61% Due 2019 [Member] | Medium-Term Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	12	12
Debt interest percentage	7.61%
Debt instrument maturity date	2019
Debt instrument, interest percentage	7.61%
Debt instrument, carrying value	12	12
Debt instrument maturity date	2019
Delmarva Power & Light Co/De [Member] | 7.72% Due 2027 [Member] | Medium-Term Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	10	10
Debt interest percentage	7.72%
Debt instrument maturity date	2027
Debt instrument, interest percentage	7.72%
Debt instrument, carrying value	10	10
Debt instrument maturity date	2027
Delmarva Power & Light Co/De [Member] | 5.00% Due 2014 [Member] | Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value		100
Debt interest percentage	5.00%
Debt instrument maturity date	2014
Debt instrument, interest percentage	5.00%
Debt instrument, carrying value		100
Debt instrument maturity date	2014
Delmarva Power & Light Co/De [Member] | 5.00% Due 2015 [Member] | Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	100	100
Debt interest percentage	5.00%
Debt instrument maturity date	2015
Debt instrument, interest percentage	5.00%
Debt instrument, carrying value	100	100
Debt instrument maturity date	2015
Potomac Capital Investment Corporation (PCI) [Member] | 6.59% - 6.69% Due 2014 [Member] | Recourse Debt [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value		11
Debt instrument maturity date	2014
Debt instrument, carrying value		11
Debt instrument maturity date	2014
Debt instrument percentage, minimum	6.59%
Debt instrument percentage, maximum	6.69%
Debt instrument percentage, minimum	6.59%
Debt instrument percentage, maximum	6.69%
Pepco Energy Services [Member] | 6.70% - 7.46% Due 2017-2018 [Member] | Secured Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	4	14
Debt instrument, carrying value	4	14
Debt instrument maturity date, start	2015
Debt instrument maturity date, end	2018
Debt instrument percentage, minimum	6.70%
Debt instrument percentage, maximum	7.46%
Debt instrument percentage, minimum	6.70%
Debt instrument percentage, maximum	7.46%
Debt instrument maturity date, start	2015
Debt instrument maturity date, end	2018
Potomac Electric Power Co [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	2,135	1,910
Net unamortized premium(discount)	(11)	(11)
Current portion of long-term debt		(175)
Total net long-term debt	2,124	1,724
Total long-term debt	2,135	1,910
Potomac Electric Power Co [Member] | 4.65% Due 2014 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	4.65%				4.65%
Debt instrument maturity date	2014
Debt instrument, interest percentage	4.65%				4.65%
Debt instrument maturity date	2014
Debt instrument, carrying value		175
Total long-term debt		175
Potomac Electric Power Co [Member] | 3.05% Due 2022 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	3.05%
Debt instrument maturity date	2022
Debt instrument, interest percentage	3.05%
Debt instrument maturity date	2022
Debt instrument, carrying value	200	200
Total long-term debt	200	200
Potomac Electric Power Co [Member] | 6.20% Due 2022 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	6.20%
Debt instrument maturity date	2022
Debt instrument, interest percentage	6.20%
Debt instrument maturity date	2022
Debt instrument, carrying value	110	110
Total long-term debt	110	110
Potomac Electric Power Co [Member] | 3.60% Due 2024 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	3.60%
Debt instrument maturity date	2024
Debt instrument, interest percentage	3.60%
Debt instrument maturity date	2024
Debt instrument, carrying value	400
Total long-term debt	400
Potomac Electric Power Co [Member] | 5.75% Due 2034 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	5.75%
Debt instrument maturity date	2034
Debt instrument, interest percentage	5.75%
Debt instrument maturity date	2034
Debt instrument, carrying value	100	100
Total long-term debt	100	100
Potomac Electric Power Co [Member] | 5.40% Due 2035 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	5.40%
Debt instrument maturity date	2035
Debt instrument, interest percentage	5.40%
Debt instrument maturity date	2035
Debt instrument, carrying value	175	175
Total long-term debt	175	175
Potomac Electric Power Co [Member] | 6.50% Due 2037 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	6.50%
Debt instrument maturity date	2037
Debt instrument, interest percentage	6.50%
Debt instrument maturity date	2037
Debt instrument, carrying value	500	500
Total long-term debt	500	500
Potomac Electric Power Co [Member] | 7.90% Due 2038 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	7.90%
Debt instrument maturity date	2038
Debt instrument, interest percentage	7.90%
Debt instrument maturity date	2038
Debt instrument, carrying value	250	250
Total long-term debt	250	250
Potomac Electric Power Co [Member] | 4.15% Due 2043 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	4.15%
Debt instrument maturity date	2043
Debt instrument, interest percentage	4.15%
Debt instrument maturity date	2043
Debt instrument, carrying value	250	250
Total long-term debt	250	250
Potomac Electric Power Co [Member] | 4.95% Due 2043 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt interest percentage	4.95%
Debt instrument maturity date	2043
Debt instrument, interest percentage	4.95%
Debt instrument maturity date	2043
Debt instrument, carrying value	150	150
Total long-term debt	$ 150	$ 150