Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net periodic benefit cost	$ 391	$ 288	$ 190
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	194	186	165
Interest cost	602	639	678
Expected return on plan assets	(788)	(808)	(806)
Recognized net actuarial loss	489	384	247
Amortization of prior service cost (benefit)	19	19	19
Settlements	9		2
Curtailments	6		(9)
Special termination benefits	77
Net periodic benefit cost	608	420	296
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	17	14	17
Interest cost	114	131	158
Expected return on plan assets			(2)
Recognized net actuarial loss	35	25	26
Amortization of prior service cost (benefit)	(18)	(16)	(17)
Net periodic benefit cost	$ 148	$ 154	$ 182