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, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	$ 100		$ 76		$ 297		$ 240
Interest cost	165		167		494		495
Expected return on plan assets	(150)		(168)		(449)		(502)
Amortization of transition obligation	0		0		0		0
Amortization of prior service cost	5		8		15		26
Amortization of unrecognized loss	29		13		92		37
Net periodic benefit cost	149		96		449		296
Less: transfer to regulatory account	(75)	[1]	(32)	[1]	(225)	[1]	(104)	[1]
Total	74		64		224		192
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	14		9		37		31
Interest cost	21		23		63		69
Expected return on plan assets	(19)		(22)		(58)		(62)
Amortization of transition obligation	6		7		18		19
Amortization of prior service cost	7		8		19		20
Amortization of unrecognized loss	1		1		4		3
Net periodic benefit cost	30		26		83		80
Less: transfer to regulatory account	0	[1]	0	[1]	0	[1]	0	[1]
Total	$ 30		$ 26		$ 83		$ 80

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