New And Significant Accounting Policies (Components Of Net Periodic Benefit Cost) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	$ 115		$ 98		$ 230		$ 197
Interest cost	156		165		312		329
Expected return on plan assets	(163)		(150)		(325)		(299)
Amortization of transition obligation	0		0		0		0
Amortization of prior service cost	5		5		10		10
Amortization of unrecognized loss	28		32		55		63
Net periodic benefit cost	141		150		282		300
Less: transfer to regulatory account	(56)	[1]	(75)	[1]	(113)	[1]	(150)	[1]
Total	85		75		169		150
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost for benefits earned	13		11		26		23
Interest cost	18		21		37		42
Expected return on plan assets	(20)		(20)		(40)		(39)
Amortization of transition obligation	0		6		0		12
Amortization of prior service cost	5		6		11		12
Amortization of unrecognized loss	2		2		3		3
Net periodic benefit cost	18		26		37		53
Less: transfer to regulatory account	0	[1]	0	[1]	0	[1]	0	[1]
Total	$ 18		$ 26		$ 37		$ 53

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