Pension plans and other postretirement benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension curtailment	$ 37.4	$ 0
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	7.0	6.9
Interest cost	12.3	13.9
Expected return on plan assets	(17.0)	(15.7)
Amortization of prior service cost	(0.4)	(1.4)
Amortization of unrecognized net loss	7.4	5.1
Settlement change	0	0.9
Curtailment charge	(37.4)	0
Net periodic benefit cost	(28.1)	9.7
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0.2	0.2
Interest cost	0.3	0.6
Amortization of prior service cost	(0.9)	(0.7)
Amortization of unrecognized net loss	(0.5)	(0.5)
Net periodic benefit cost	$ (0.9)	$ (0.4)