Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Sep. 30, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts receivable	$ 99	$ 91
Common stock, par value per share	$ 0.50	$ 0.50
Common stock, shares authorized	1,200,000,000	1,200,000,000
Common stock, shares issued	953,354,012	953,354,012
Common stock, shares outstanding	634,221,544	641,691,971
Treasury stock, shares	319,132,468	311,662,041