Components of Net Periodic Benefit Cost, as well as Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income for Qualified Plan and SERP (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Service cost	$ 11	$ 10	$ 10
Interest cost	14	14	12
Expected return on plan assets	(16)	(14)	(12)
Amortization of actuarial loss and prior service cost	4	2	1
Net periodic benefit cost	13	12	11
Current year actuarial loss	30	0	15
Recognition of actuarial loss	(4)	(2)	0
Recognition of prior service cost	(1)	(1)	(1)
Total loss (gain) recognized in other comprehensive income	$ 25	$ (3)	$ 14