Amounts Recognized In Other Comprehensive Loss and Accumulated Other Comprehensive Loss Related To Postretirement Benefit Plans and Expected Costs to be Recognized in Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Amounts Recognized In Other Comprehensive Loss Related To Postretirement Benefit Plans [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	$ (3,135)	$ (2,848)	$ (921)
Prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(69)	(10)	(62)
Total Incurred but Not Recognized	(3,204)	(2,858)	(983)
Actuarial (gains) and losses - Recognition of Previously Deferred Amounts	819	624	501
Prior service (credit) and cost - Recognition of Previously Deferred Amounts	39	42	52
Total Reclassification Adjustment for Prior Period Amounts Recognized	858	666	553
Qualified Defined Benefit Pension Plans
Amounts Recognized In Other Comprehensive Loss Related To Postretirement Benefit Plans [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(2,933)	(2,793)	(763)
Prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(73)	(3)	(61)
Actuarial (gains) and losses - Recognition of Previously Deferred Amounts	721	568	464
Prior service (credit) and cost - Recognition of Previously Deferred Amounts	47	53	62
Retiree Medical And Life Insurance Plans
Amounts Recognized In Other Comprehensive Loss Related To Postretirement Benefit Plans [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(104)	1	(95)
Prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	4	(7)
Actuarial (gains) and losses - Recognition of Previously Deferred Amounts	21	22	17
Prior service (credit) and cost - Recognition of Previously Deferred Amounts	(8)	(11)	(10)
Other Plans
Amounts Recognized In Other Comprehensive Loss Related To Postretirement Benefit Plans [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(98)	(56)	(63)
Prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost			(1)
Actuarial (gains) and losses - Recognition of Previously Deferred Amounts	$ 77	$ 34	$ 20