Pension and Postretirement Benefits - Additional Information (Detail) - USD ($)	1 Months Ended
	Jul. 31, 2018	Jun. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Estimated contribution to pension plans		$ 162,400,000
Underfunded Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated contribution to pension plans		12,400,000
Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated contribution to pension plans		$ 150,000,000
Qualified Pension Plan [Member] | Subsequent Event [Member]
Defined Benefit Plan Disclosure [Line Items]
Contribution made to qualified pension plans	$ 75,000,000