New And Significant Accounting Policies (Components Of Net Periodic Benefit Cost) (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
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	$ 92		$ 121		$ 287		$ 351
Interest cost	175		158		521		470
Expected return on plan assets	(202)		(162)		(605)		(487)
Amortization of prior service cost	5		5		15		15
Amortization of net actuarial loss	1		28		2		83
Net periodic benefit cost	71		150		220		432
Less: transfer to regulatory account	13	[1]	(66)	[1]	31	[1]	(179)	[1]
Total	84		84		251		253
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	12		14		34		40
Interest cost	19		19		57		56
Expected return on plan assets	(25)		(20)		(77)		(60)
Amortization of prior service cost	6		6		17		17
Amortization of net actuarial loss	1		1		2		4
Net periodic benefit cost	13		20		33		57
Less: transfer to regulatory account	0	[1]	0	[1]	0	[1]	0	[1]
Total	$ 13		$ 20		$ 33		$ 57

[1] The Utility recorded these amounts to a regulatory account since they are probable of recovery from customers in futures rates.