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 Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 121	$ 99	$ 88
Interest cost	191	184	178
Expected return on plan assets	(163)	(138)	(140)
Curtailment loss	2
Amortization of prior service credits		(1)	(2)
Settlement (gain) loss	(10)	1	1
Amortization of unrecognized actuarial (gain) loss	48	21	(20)
Net periodic benefit cost	189	166	105
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	52	50	47
Interest cost	110	124	127
Expected return on plan assets	(2)	(2)	(2)
Curtailment loss	2
Amortization of prior service credits	(3)
Amortization of unrecognized actuarial (gain) loss	3	(3)	(2)
Net periodic benefit cost	$ 162	$ 169	$ 170