Retirement Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 67	$ 57	$ 73
Interest cost	102	100	89
Expected return on plan assets	(168)	(161)	(141)
Amortization of unrecognized net actuarial losses	75	32	61
Settlement loss	17	24	0
Curtailment loss	0	0	1
Special termination benefit recognized	1	1	5
Net periodic benefit cost	94	53	88
Postretirement Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	4	4
Interest cost	3	3	3
Expected return on plan assets	0	0	0
Amortization of unrecognized net actuarial losses	0	0	1
Settlement loss	0	0	0
Curtailment loss	0	0	0
Special termination benefit recognized	0	0	0
Net periodic benefit cost	$ 7	$ 7	$ 8