Pension and Other Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 555	$ 619	$ 584
Interest cost	661	718	688
Expected return on plan assets	(970)	(972)	(891)
Net amortization	185	201	148
Termination benefits	27	59	54
Curtailments	(10)	(86)	(50)
Settlements	18	4	(1)
Net periodic benefit cost	466	543	532
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	82	110	108
Interest cost	121	141	148
Expected return on plan assets	(136)	(142)	(132)
Net amortization	(35)	(17)	8
Termination benefits	18	29	42
Curtailments	(7)	1	(10)
Settlements
Net periodic benefit cost	$ 43	$ 122	$ 164