Change in Benefit Obligations (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Pension Plans, Defined Benefit
Benefit obligation, beginning of year	$ 2,661	[1]	$ 2,261
Service cost	0		62
Interest cost	119		128
Plan participants' contributions	0		0
Actuarial (gain)/loss	242		415
Benefits paid	(184)		(109)
Less federal Medicare drug subsidy	0		0
Curtailments	0		(96)
Benefit obligation, end of year	2,838	[1]	2,661	[1]
Other Postretirement Benefit Plans, Defined Benefit
Benefit obligation, beginning of year	173	[1]	189
Service cost	0		0
Interest cost	7		9
Plan participants' contributions	22		22
Actuarial (gain)/loss	(2)		(17)
Benefits paid	(36)		(33)
Less federal Medicare drug subsidy	3		3
Curtailments	0		0
Benefit obligation, end of year	$ 167	[1]	$ 173	[1]

[1] 1Includes $91 million and $107 million of benefit obligations for the unfunded nonqualified supplemental pension plans as of December 31, 2012 and 2011, respectively.