Amounts Recognized for Pension and Postretirement Benefits in Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Compensation and Retirement Disclosure [Abstract]
Amortization of prior service cost included in net periodic pension and postretirement cost, Before-tax amount	$ (2)	$ (2)	$ (4)	$ (4)
Amortization of actuarial loss included in net periodic pension and postretirement cost, Before-tax amount	5	7	14	21
Other comprehensive income - pension benefits, Before-tax amount	3	5	10	17
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	(1)	(2)	(2)	(4)
Other comprehensive - pension benefits, Tax Benefit	(1)	(2)	(2)	(4)
Amortization of prior service cost included in net periodic pension and postretirement cost, Net-of-tax Amount	(2)	(2)	(4)	(4)
Amortization of actuarial loss included in net periodic pension and postretirement cost, Net-of-tax Amount	4	5	12	17
Other comprehensive income - pension benefits, Net-of-tax Amount	$ 2	$ 3	$ 8	$ 13