Pension and Other Postretirement Benefits - Additional Information (Detail)	3 Months Ended	9 Months Ended
	Sep. 30, 2016 USD ($) Installments	Sep. 30, 2016 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Increase in pension liability, separation transaction		$ 845,000,000
Accumulated increase in net actuarial loss after-tax, separation transaction		(551,000,000)
Decrease in net periodic benefit cost, separation transaction	$ 5,000,000
Cash contribution term to pension plan	30 months
Number of installments | Installments	3
Minimum required cash contribution to pension plan	$ 50,000,000
Aggregate cash cash contribution to pension plan	150,000,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in interest cost component of net periodic benefit cost determination	22,000,000	70,000,000
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in interest cost component of net periodic benefit cost determination	$ 4,000,000	$ 12,000,000