Changes in Balance of Accumulated Other Comprehensive Loss (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Postretirement Benefit and Other Adjustments Recognized in Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (11,257)	$ (9,010)	$ (8,595)
Other comprehensive (loss) income	(2,236)	(2,247)	(415)
Ending balance	(13,493)	(11,257)	(9,010)
Postretirement Benefit Plan Adjustments
Schedule of Postretirement Benefit and Other Adjustments Recognized in Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(11,186)	(8,994)	(8,564)
Other comprehensive (loss) income	(2,346)	(2,192)	(430)
Ending balance	(13,532)	(11,186)	(8,994)
Other, net
Schedule of Postretirement Benefit and Other Adjustments Recognized in Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(71)	(16)	(31)
Other comprehensive (loss) income	110	(55)	15
Ending balance	$ 39	$ (71)	$ (16)