Post Retirement Benefit Plans - Components of Net Periodic Pension Cost (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2018	Apr. 30, 2017
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3.3	$ 3.3	$ 6.6	$ 6.6
Interest cost	4.6	4.6	9.2	9.2
Expected return on plan assets	(6.1)	(7.1)	(12.2)	(14.2)
Amortization of prior service cost and net actuarial gain	3.6	2.8	7.2	5.6
Net periodic costs (benefits) for pension and post-retirement benefits	5.4	3.6	10.8	7.2
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Interest cost	0.1	0.1	0.2	0.2
Amortization of prior service cost and net actuarial gain	(0.4)	(0.4)	(0.8)	(0.7)
Net periodic costs (benefits) for pension and post-retirement benefits	$ (0.3)	$ (0.3)	$ (0.6)	$ (0.5)