Financial Risk Management Activities (Schedule Providing Credit Risk From Others, Net Of Collateral) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Nonaffiliated [Member] | Investment Grade - External Rating [Member]
Derivative [Line Items]
Net exposure	$ 31	[1]
Power [Member]
Derivative [Line Items]
Current Exposure	91
Securities held as Collateral	27
Net exposure	79
Number of Counterparties greater than 10%	2
Amount Of Net Credit Exposure Greater Than Ten Percent	52
Power [Member] | Investment Grade - External Rating [Member]
Derivative [Line Items]
Current Exposure	89
Securities held as Collateral	27
Net exposure	77
Number of Counterparties greater than 10%	2
Amount Of Net Credit Exposure Greater Than Ten Percent	52	[1]
Power [Member] | Non-Investment Grade - External Rating [Member]
Derivative [Line Items]
Current Exposure	1
Securities held as Collateral	0
Net exposure	1
Number of Counterparties greater than 10%	0
Amount Of Net Credit Exposure Greater Than Ten Percent	0
Power [Member] | Investment Grade - No External Rating [Member]
Derivative [Line Items]
Current Exposure	1
Securities held as Collateral	0
Net exposure	1
Number of Counterparties greater than 10%	0
Amount Of Net Credit Exposure Greater Than Ten Percent	0
Power [Member] | Non-Investment Grade - No External Rating [Member]
Derivative [Line Items]
Current Exposure	0
Securities held as Collateral	0
Net exposure	0
Number of Counterparties greater than 10%	0
Amount Of Net Credit Exposure Greater Than Ten Percent	0
PSE And G [Member] | Investment Grade - External Rating [Member]
Derivative [Line Items]
Net exposure	$ 21	[1]

[1] (A)Includes net exposure of $21 million with PS