Consolidated Statement of Shareowners' Equity Consolidated Statement of Shareowners' Equity - USD ($) $ in Millions	Total	Common Stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive loss	Common stock in treasury, at cost
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of accounting standard				$ 0.0
Balance at beginning of period at Sep. 30, 2017		$ 181.4	$ 1,638.0	6,103.4	$ (1,179.2)	$ (4,080.0)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense			27.3
Shares delivered under incentive plans			4.4
Net income	$ 189.6			189.6
Cash dividends ($1.94, $1.84, $3.88, and $3.51 per share)				(441.5)
Other comprehensive income	38.7				38.7
Purchases						(1,104.8)
Shares delivered under incentive plans						66.9
Balance at end of period at Jun. 30, 2018	1,444.2		1,669.7	5,851.5	(1,140.5)	(5,117.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of accounting standard				0.0
Balance at beginning of period at Mar. 31, 2018		181.4	1,659.6	5,880.9	(1,081.5)	(4,693.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense			9.9
Shares delivered under incentive plans			0.2
Net income	198.6			198.6
Cash dividends ($1.94, $1.84, $3.88, and $3.51 per share)				(228.0)
Other comprehensive income	(59.0)				(59.0)
Purchases						(430.8)
Shares delivered under incentive plans						6.1
Balance at end of period at Jun. 30, 2018	1,444.2		1,669.7	5,851.5	(1,140.5)	(5,117.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of accounting standard				6.1
Balance at beginning of period at Sep. 30, 2018	1,617.5	181.4	1,681.4	6,198.1	(941.9)	(5,501.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense			31.4
Shares delivered under incentive plans			(14.8)
Net income	687.7			687.7
Cash dividends ($1.94, $1.84, $3.88, and $3.51 per share)				(460.3)
Other comprehensive income	11.7				11.7
Purchases						(775.1)
Shares delivered under incentive plans						52.3
Balance at end of period at Jun. 30, 2019	1,156.5		1,698.0	6,431.6	(930.2)	(6,224.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of accounting standard				0.0
Balance at beginning of period at Mar. 31, 2019		$ 181.4	1,686.7	6,398.0	(940.3)	(5,989.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense			10.6
Shares delivered under incentive plans			0.7
Net income	261.4			261.4
Cash dividends ($1.94, $1.84, $3.88, and $3.51 per share)				(227.8)
Other comprehensive income	10.1				10.1
Purchases						(246.3)
Shares delivered under incentive plans						11.5
Balance at end of period at Jun. 30, 2019	$ 1,156.5		$ 1,698.0	$ 6,431.6	$ (930.2)	$ (6,224.3)