Employee Benefit Plans - Components of Net Periodic Benefit Costs (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 10	$ 10	$ 8
Interest Cost	16	15	15
Expected Return on Plan Assets	(17)	(16)	(14)
Recognized Actuarial Loss	7	6	5
Net Periodic Benefit Cost	16	15	14
Other Retiree Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	3	3	3
Interest Cost	3	4	4
Prior Service Cost Amortization		(1)	(2)
Net Periodic Benefit Cost	$ 6	$ 6	$ 5