Fair Value Measurements - Schedule of financial instruments not measured at fair value (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014		Dec. 31, 2013	Sep. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 7,885.2		$ 7,596.0		$ 6,699.7	$ 6,323.1
Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	7,758.0		7,476.8
Other Investments	141.6	[1]	75.6	[1]
Debt	1,198.3		1,198.2
Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	7,758.0		7,476.8
Other Investments	150.4	[1]	87.8	[1]
Debt	$ 1,239.5		$ 1,235.8
Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Level	2
Cash and Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Level	1
Other Investments [Member] | Time Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Level	2
Other Investments [Member] | Cost-method Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Level	3

[1] Primarily consist of Level 3 assets.