Share-Based Compensation Summary of Options Exercised (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Proceeds from Stock Options Exercised	$ 14	$ 50	$ 75
Actual tax benefit realized for tax deductions from stock option exercises	8	17	20
Total intrinsic value of stock options exercised	20	51	52
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value	$ 2	$ 11	$ 59