Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Pension Plans, Defined Benefit
Service cost	$ 0	$ 17	$ 0	$ 35
Interest cost	31	32	60	64
Expected return on plan assets	(43)	(47)	(86)	(94)
Amortization of prior service cost	0	(4)	0	(9)
Recognized net actuarial loss	6	11	12	21
Net periodic benefit cost	(6)	9	(14)	17
Other Postretirement Benefit Plans, Defined Benefit
Service cost	0	0	0	0
Interest cost	1	2	3	5
Expected return on plan assets	(1)	(2)	(3)	(4)
Amortization of prior service cost	0	0	0	0
Recognized net actuarial loss	0	0	0	0
Net periodic benefit cost	$ 0	$ 0	$ 0	$ 1