Fair Value Measurement (Details Textual) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Offsetting Derivative Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 59.8	$ 26.3	$ 19.1
Derivative Asset, Offset Amount	(6.0)	(2.1)	(7.7)
Derivative Asset, Fair Value, Gross Liability	0	(1.7)	(0.3)
Derivative, Collateral, Right to Reclaim Cash	0	0	0
Derivative Assets, Net Presentation	53.8	22.5	11.1
Derivative Assets	53.8	24.2	11.4
Derivative Liability, Fair Value, Gross Liability	(49.2)	(57.5)	(128.8)
Derivative Liability, Offset Amount	6.0	2.1	7.7
Derivative Liability, Fair Value, Gross Asset	0	1.7	0.3
Derivative, Collateral, Obligation to Return Cash	0	1.4	5.4
Derivative Liability, Net Presentation	(43.2)	(52.3)	(115.4)
Derivative Liabilities	(43.2)	(55.4)	(121.1)
Carrying value long-term debt	3,616.3		3,522.8
Estimated fair value long-term debt	$ 3,856.9		$ 3,840.3