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, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	$ 121		$ 100		$ 351		$ 297
Interest cost	158		165		470		494
Expected return on plan assets	(162)		(150)		(487)		(449)
Amortization of transition obligation	0		0		0		0
Amortization of prior service cost	5		5		15		15
Amortization of net actuarial loss	28		29		83		92
Net periodic benefit cost	150		149		432		449
Less: transfer to regulatory account	(66)	[1]	(75)	[1]	(179)	[1]	(225)	[1]
Total	84		74		253		224
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	14		14		40		37
Interest cost	19		21		56		63
Expected return on plan assets	(20)		(19)		(60)		(58)
Amortization of transition obligation	0		6		0		18
Amortization of prior service cost	6		7		17		19
Amortization of net actuarial loss	1		1		4		4
Net periodic benefit cost	20		30		57		83
Less: transfer to regulatory account	0	[1]	0	[1]	0	[1]	0	[1]
Total	$ 20		$ 30		$ 57		$ 83

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