Pension Plans and Other Postretirement Benefits (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pension Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	$ 21	$ 19
Interest cost	20	21
Expected return on plan assets	(23)	(23)
Amortization of net actuarial loss (gain)	29	23
Net periodic benefit cost	47	40
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	2	2
Interest cost	4	4
Net periodic benefit cost	$ 6	$ 6