Pension and Other Postretirement Benefit Plans - Components of Net Cost of Defined Benefit Plans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 133	$ 158	$ 416	$ 461
Interest cost	162	182	494	541
Expected return on plan assets	(239)	(243)	(727)	(728)
Net amortization	48	58	144	149
Termination benefits	4	15	13	32
Curtailments	(4)	(6)	(5)	(16)
Settlements				(1)
Net periodic benefit cost	104	164	335	438
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	22	27	64	83
Interest cost	31	35	93	106
Expected return on plan assets	(34)	(35)	(102)	(106)
Net amortization	(9)	(4)	(25)	(13)
Termination benefits	5	5	10	11
Curtailments	(2)	(1)	(6)
Net periodic benefit cost	$ 13	$ 27	$ 34	$ 81