Employee Retirement Plans - Narrative (Details) - USD ($)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plan Disclosure
Amortization of prior service credits	$ 500,000
Pension Benefits
Defined Benefit Plan Disclosure
Contribution made to Pension Plan	14,600,000	$ 11,400,000
Projected benefit obligations of unfunded and non qualified supplemental executive retirement plans	697,800,000	707,700,000	$ 614,700,000
Pre-tax cost to sponsor unfunded and non-qualified supplemental executive retirement plans	18,900,000	14,500,000	12,800,000
Net actuarial loss	21,300,000	31,400,000
Fair value of pension and other postretirement benefit contributions	0	0
Supplemental Employee Retirement Plans
Defined Benefit Plan Disclosure
Expected amortization of net actuarial losses	1,100,000
Projected benefit obligations of unfunded and non qualified supplemental executive retirement plans	50,700,000	47,400,000
Pre-tax cost to sponsor unfunded and non-qualified supplemental executive retirement plans	3,100,000	2,600,000	2,300,000
Net actuarial loss	11,300,000	13,000,000
Pension and other postretirement benefit contributions	1,300,000	400,000	0
Fair value of pension and other postretirement benefit contributions	31,800,000	28,400,000
U.S. Pension Plan | Pension Benefits
Defined Benefit Plan Disclosure
Expected amortization of net actuarial losses	13,500,000
ABO for the pension plans	605,200,000	601,300,000
Contribution made to Pension Plan	$ 11,400,000	$ 9,900,000	$ 11,100,000