Fair Value Measurements - Schedule of Financial Instruments not Measured at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2017	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 8,786.2	$ 8,483.3	$ 8,242.1	$ 8,368.1
Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	8,564.8	8,247.1
Other investments	52.8	131.6
Cost method investments	54.6	50.0
Senior notes	1,343.8	1,348.5
Loan	30.9	52.7
Estimated Fair Value [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	8,564.8	8,247.1
Estimated Fair Value [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	52.8	131.6
Senior notes	1,373.8	1,412.5
Loan	30.9	52.7
Estimated Fair Value [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost method investments	$ 73.9	$ 61.3