Derivatives (Gains And Losses On Derivative Instruments) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Net unrealized gain - regulatory assets and liabilities	$ (6)	[1]	$ 40	[1]	$ 79	[1]	$ 115	[1]
Realized loss - cost of electricity	(22)	[2]	(57)	[2]	(48)	[2]	(136)	[2]
Realized loss - cost of natural gas	(4)	[2]	(2)	[2]	(7)	[2]	(14)	[2]
Total commodity risk	$ (32)		$ (19)		$ 24		$ (35)

[1] Unrealized gains and losses on commodity risk-related derivative instruments are recorded to regulatory liabilities or assets, respectively, rather than being recorded to the Condensed Consolidated Statements of Income. These amounts exclude the impact of cash collateral postings.

[2] These amounts are fully passed through to customers in rates. Accordingly, net income was not impacted by realized amounts on these instruments.