Commitments And Contingent Liabilities (New Generation And Development) (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012 MW	Jun. 30, 2011
Long-term Purchase Commitment [Line Items]
Total expenditures to date	$ 1,280	$ 1,002
Approximately amount of MW's already installed	30
Estimated total cost of land and buildings owned phase	194
Number of MW of solar capacity placed into service	36
Energy Holdings-Solar [Member]
Long-term Purchase Commitment [Line Items]
Guarantee payment of obligations	71.5
Sites acquired during period, MW	25
Guarantee obligations outstanding	23
Estimated project costs	75
Power [Member]
Long-term Purchase Commitment [Line Items]
Total expenditures to date	344	323
Power [Member] | Nuclear Steam Path Capital Additions [Member]
Long-term Purchase Commitment [Line Items]
Approximate amount committed	192
Increase of MW nominal capacity after completion of upgrades	14
Total expenditures to date	127
Power [Member] | Nuclear Up Rate Capital Additions [Member] | Peach Bottom Units [Member]
Long-term Purchase Commitment [Line Items]
Approximate amount committed	419
Increase of MW nominal capacity after completion of upgrades	130
Total expenditures to date	44
Power [Member] | Connecticut Capital Additions [Member]
Long-term Purchase Commitment [Line Items]
Number of MW of gas fired peaking capacity to be built	130
Long term purchase commitment amount low range	149
Power [Member] | PJM Interconnection Capital Additions [Member]
Long-term Purchase Commitment [Line Items]
Total expenditures to date	244
Power [Member] | PJM Interconnection Capital Additions [Member] | Period 2013-2015 [Member]
Long-term Purchase Commitment [Line Items]
Number of MW of gas fired peaking capacity to be built	267
PSE And G [Member]
Long-term Purchase Commitment [Line Items]
Total expenditures to date	870	674
Number of MW of solar generation on existing utility poles being installed	40
Total project cost	262
Number of MW of installation of solar generation on land and building	40
PSE And G [Member] | Solar Capital Additions [Member]
Long-term Purchase Commitment [Line Items]
Total expenditures to date	215
Investment in projects, amount	$ 173