Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Plans, Defined Benefit
Service cost	$ 0	$ 18
Interest cost	29	32
Expected return on plan assets	(43)	(47)
Amortization of prior service cost	0	(5)
Recognized net actuarial loss	6	10
Net periodic benefit cost	(8)	8
Other Postretirement Benefit Plans, Defined Benefit
Service cost	0	0
Interest cost	2	3
Expected return on plan assets	(2)	(2)
Amortization of prior service cost	0	0
Recognized net actuarial loss	0	0
Net periodic benefit cost	$ 0	$ 1