Derivative Instruments and Fair Value Measurement (Details 2) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, carrying amount	$ 1,175.1	$ 1,200.9	$ 1,024.7	$ 903.9
Cash and cash equivalents, fair value	1,175.1	1,200.9
Short-term investments, carrying amount	574.4	372.7
Short-term investments, fair value	574.4	372.7
Short-term debt, carrying amount	279.9	179.0
Short-term debt, fair value	279.9	179.0
Long-term debt, carrying amount	905.4	905.1
Long-term debt, fair value	1,106.2	1,072.2
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	1,110.3	1,079.0
Short-term investments, fair value	0	0
Short-term debt, fair value	0	0
Long-term debt, fair value	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	64.8	121.9
Short-term investments, fair value	574.4	372.7
Short-term debt, fair value	279.9	179.0
Long-term debt, fair value	1,106.2	1,072.2
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	0	0
Short-term investments, fair value	0	0
Short-term debt, fair value	0	0
Long-term debt, fair value	$ 0	$ 0