Pension And Other Postretirement Benefits (Schedule Of Changes In Benefit Obligations And Plan Assets) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Change in Benefit Obligation
Benefit obligation at end of year	$ 2,300		$ 2,000
Change in Plan Assets
Fair value of plan assets at end of year	2,360		1,975
Pension Benefits [Member]
Change in Benefit Obligation
Benefit obligation at beginning of year	2,124		1,970
Service cost	35		35		35
Interest cost	107		107		110
Amendments			18
Actuarial loss (gain)	341		176
Benefits paid	(113)	[1]	(182)	[1]
Termination benefits					3
Benefit obligation at end of year	2,494		2,124		1,970
Change in Plan Assets
Fair value of plan assets at beginning of year	1,694		1,632
Actual return on plan assets	252		127
Company contributions	206		117
Benefits paid	(113)	[1]	(182)	[1]
Fair value of plan assets at end of year	2,039		1,694		1,632
Funded Status at end of year (plan assets less plan obligations)	(455)		(430)
Other Postretirement Benefits [Member]
Change in Benefit Obligation
Benefit obligation at beginning of year	750		704
Service cost	7		5		5
Interest cost	35		37		39
Amendments			7
Actuarial loss (gain)	24		36
Benefits paid	(41)	[1]	(40)	[1]
Termination benefits	1		1		6
Benefit obligation at end of year	775		750		704
Change in Plan Assets
Fair value of plan assets at beginning of year	281		275
Actual return on plan assets	38
Company contributions	43		46
Benefits paid	(41)	[1]	(40)	[1]
Fair value of plan assets at end of year	321		281		275
Funded Status at end of year (plan assets less plan obligations)	$ (454)		$ (469)

[1] Other Postretirement Benefits paid is net of Medicare Part D subsidy receipts of $4 million and $2 million in 2012 and in 2011, respectively.