Pension Plans and Other Postretirement Benefits (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Pension Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	$ 25	$ 21
Interest cost	25	20
Expected return on plan assets	(27)	(23)
Amortization of net actuarial loss (gain)	9	29
Net periodic benefit cost	32	47
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	2	2
Interest cost	4	4
Expected return on plan assets	0	0
Amortization of net actuarial loss (gain)	(2)	0
Net periodic benefit cost	$ 4	$ 6