Fair Value Measurements - Fair Value of Financial Assets and Liabilities Measured on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Dec. 31, 2017	Sep. 30, 2017
Level 1 | Deferred compensation plan investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Asset (Liability)	$ 69	$ 63
Level 2 | Foreign currency forward exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Asset (Liability)	(5)	(7)
Level 2 | Deferred compensation plan investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Asset (Liability)	26	24
Level 2 | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Asset (Liability)	10	14
Fair Value Asset (Liability)	(1)	0
Level 2 | Foreign currency forward exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Asset (Liability)	5	8
Level 3 | Acquisition-related contingent consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Asset (Liability)	$ (16)	$ (17)