Retirement Plans (Schedule of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 30, 2016	Dec. 29, 2017	Sep. 30, 2016	Sep. 25, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	$ 0.0		$ 0.0	$ 0.0
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.8	$ 1.4	1.8	2.4
Interest cost	2.0	2.3	13.2	14.5
Expected return on plan assets	(2.3)	(1.3)	(16.7)	(18.9)
Amortization of net actuarial loss	3.5	2.7	11.3	9.2
Amortization of prior service cost	0.1	0.2	0.0	0.0
Loss on plan settlements	45.0	71.1	8.1	5.9
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment		(1.0)
Net period benefit cost (credit)	49.1	75.4	17.7	13.1
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.0	0.1	0.1
Interest cost	0.4	1.7	2.0	1.9
Amortization of prior service cost	(0.5)	(2.0)	(2.1)	(4.0)
Loss on plan settlements	0.0	(0.9)	0.0	0.0
Net period benefit cost (credit)	$ 0.0	$ (1.2)	$ 0.0	$ (2.0)