Net Periodic Benefit Cost for Pension and Postretirement Benefit Plans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
U.S. Pension Benefits
Net Periodic Cost:
Service cost	$ 338	$ 249
Interest cost	362	353
Expected return on assets	(537)	(492)
Amortization of:
Transition obligation	0	0
Other net (gain) loss	0	0
Prior service cost	43	43
Actuarial (gain) loss	0	0
Net periodic benefit cost	206	153
U.S. Postretirement Medical Benefits
Net Periodic Cost:
Service cost	26	22
Interest cost	46	52
Expected return on assets	(8)	(4)
Amortization of:
Transition obligation	0	0
Other net (gain) loss	0	0
Prior service cost	1	1
Actuarial (gain) loss	0	0
Net periodic benefit cost	65	71
International Pension Benefits
Net Periodic Cost:
Service cost	15	15
Interest cost	11	11
Expected return on assets	(14)	(12)
Amortization of:
Transition obligation	0	0
Other net (gain) loss	0	0
Prior service cost	0	0
Actuarial (gain) loss	0	0
Net periodic benefit cost	$ 12	$ 14