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
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 95	$ 110	$ 94
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	53	35	35
Interest cost	100	107	107
Expected return on plan assets	(145)	(132)	(128)
Amortization of prior service cost (credit)	2	1
Amortization of net actuarial loss	67	64	47
Termination benefits
Net periodic benefit cost	77	75	61
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	8	7	5
Interest cost	29	35	37
Expected return on plan assets	(20)	(18)	(19)
Amortization of prior service cost (credit)	(11)	(4)	(5)
Amortization of net actuarial loss	12	14	14
Termination benefits		1	1
Net periodic benefit cost	$ 18	$ 35	$ 33