Pension Plans, Postretirement and Other Employee Benefits - Amounts Recognized for Pension and Postretirement Benefits in Other Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Change in total actuarial loss, Before-tax amount	$ 51	$ (7)
Amortization of prior service cost included in net periodic pension and postretirement cost, Before-tax amount	(1)	(3)
Amortization of actuarial loss included in net periodic pension and postretirement cost, Before-tax amount	20	23
Other comprehensive income - pension benefits, Before-tax amount	70	13
Change in total actuarial loss, Tax Benefit	(21)	2
Amortization of prior service cost included in net periodic pension and postretirement cost, Tax Benefit	0	0
Amortization of actuarial loss included in net periodic pension and postretirement cost, Tax Benefit	(8)	(4)
Other comprehensive - pension benefits, Tax Benefit	(29)	(2)
Change in total actuarial loss, Net-of-tax amount	30	(5)
Amortization of prior service cost included in net periodic pension and postretirement cost, Net-of-tax Amount	(1)	(3)
Amortization of actuarial loss included in net periodic pension and postretirement cost, Net-of-tax Amount	12	19
Other comprehensive income - pension benefits, Net-of-tax Amount	$ 41	$ 11	$ (80)