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Financial Instruments (Net Investment Hedge) (Details) € in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Jan. 31, 2019 EUR (€)
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) to other comprehensive income, pretax	$ 32	$ (1)	$ 13	$ 0
Foreign Exchange Contract [Member] \| Net Investment Hedging [Member] \| Other Comprehensive Income (Loss) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) to other comprehensive income, pretax	6
Gain (loss) to other comprehensive income, after-tax	$ 5
1.25 Percent Notes Due October 2025 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Debt, face amount \| €					€ 500
Notes interest rate, percentage					1.25%
2.0 Percent Notes Due October 2029 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Debt, face amount \| €					€ 500
Notes interest rate, percentage					2.00%