Amounts Recognized for Pension and Postretirement Benefits in Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Compensation and Retirement Disclosure [Abstract]
Amortization of prior service cost included in net periodic pension and postretirement cost, Before-tax amount	$ (1)	$ (1)	$ (2)	$ (2)
Amortization of actuarial loss included in net periodic pension and postretirement cost, Before-tax amount	7	6	13	11
Other comprehensive income - pension benefits, Before-tax amount	6	5	11	9
Amortization of prior service cost included in net periodic pension and postretirement cost, Tax Benefit	0	0	0	0
Amortization of actuarial loss included in net periodic pension and postretirement cost, Tax Benefit	0	0	(1)	(1)
Other comprehensive - pension benefits, Tax Benefit	0	0	(1)	(1)
Amortization of prior service cost included in net periodic pension and postretirement cost, Net-of-tax Amount	(1)	(1)	(2)	(2)
Amortization of actuarial loss included in net periodic pension and postretirement cost, Net-of-tax Amount	7	6	12	10
Other comprehensive income - pension benefits, Net-of-tax Amount	$ 6	$ 5	$ 10	$ 8