Retirement Plans - Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Settlement Payments	$ (55)
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	57	73	74
Interest cost	100	89	88
Expected return on plan assets	(161)	(141)	(116)
Amortization of unrecognized net actuarial losses	31	61	83
Settlement Payments	24		9
Curtailment loss		1
Special termination benefit recognized	1	5
Net periodic benefit cost	52	88	138
Postretirement Medical Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	4	7
Interest cost	3	3	5
Amortization of unrecognized net actuarial losses		1	2
Net periodic benefit cost	$ 7	$ 8	$ 14