Net Periodic Pension Cost for Defined-Benefit Pension Plans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Qualified
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1	$ 4	$ 2
Interest cost	12	12	32	34
Expected return on plan assets	(10)	(9)	(27)	(25)
Amortization of net loss	4	2	11	7
Net periodic pension cost	7	6	20	18
Non-Qualified
Defined Benefit Plan Disclosure [Line Items]
Interest cost	2	2	5	6
Amortization of net loss		1	1	1
Net periodic pension cost	$ 2	$ 3	$ 6	$ 7