Amounts Recognized for Pension and Postretirement Benefits in Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Change in total actuarial loss, Before-tax amount	$ 113	$ (66)
Amortization of prior service cost included in net periodic pension and postretirement cost, Before-tax amount	(5)	(4)
Amortization of actuarial loss included in net periodic pension and postretirement cost, Before-tax amount	23	20
Other comprehensive income - pension benefits, Before-tax amount	131	(50)
Change in total actuarial loss, Tax Benefit	(41)	22
Amortization of prior service cost included in net periodic pension and postretirement cost, Tax Benefit	2	2
Amortization of actuarial loss included in net periodic pension and postretirement cost, Tax Benefit	(7)	(6)
Other comprehensive - pension benefits, Tax Benefit	(46)	18
Change in total actuarial loss, Net-of-tax amount	72	(44)
Amortization of prior service cost included in net periodic pension and postretirement cost, Net-of-tax Amount	(3)	(2)
Amortization of actuarial loss included in net periodic pension and postretirement cost, Net-of-tax Amount	16	14
Other comprehensive income - pension benefits, Net-of-tax Amount	$ 85	$ (32)	$ (102)