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			17.4
Shares delivered under incentive plans			4.2
Net income (loss)	$ (9.0)			(9.0)
Cash dividends ($0.97, $0.835, $1.94, and $1.67 per share)				(213.5)
Other comprehensive income	97.7				97.7
Purchases						(674.0)
Shares delivered under incentive plans						60.8
Balance at end of period at Mar. 31, 2018	1,947.2		1,659.6	5,880.9	(1,081.5)	(4,693.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of accounting standard				0.0
Balance at beginning of period at Dec. 31, 2017		181.4	1,642.9	5,759.7	(1,175.7)	(4,252.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense			9.6
Shares delivered under incentive plans			7.1
Net income (loss)	227.4			227.4
Cash dividends ($0.97, $0.835, $1.94, and $1.67 per share)				(106.2)
Other comprehensive income	94.2				94.2
Purchases						(465.4)
Shares delivered under incentive plans						24.3
Balance at end of period at Mar. 31, 2018	1,947.2		1,659.6	5,880.9	(1,081.5)	(4,693.2)
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			20.8
Shares delivered under incentive plans			(15.5)
Net income (loss)	426.3			426.3
Cash dividends ($0.97, $0.835, $1.94, and $1.67 per share)				(232.5)
Other comprehensive income	1.6				1.6
Purchases						(528.8)
Shares delivered under incentive plans						40.8
Balance at end of period at Mar. 31, 2019	1,336.3		1,686.7	6,398.0	(940.3)	(5,989.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of accounting standard				0.0
Balance at beginning of period at Dec. 31, 2018		$ 181.4	1,674.4	6,167.6	(976.9)	(5,772.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation expense			10.5
Shares delivered under incentive plans			1.8
Net income (loss)	346.0			346.0
Cash dividends ($0.97, $0.835, $1.94, and $1.67 per share)				(115.6)
Other comprehensive income	36.6				36.6
Purchases						(236.0)
Shares delivered under incentive plans						18.7
Balance at end of period at Mar. 31, 2019	$ 1,336.3		$ 1,686.7	$ 6,398.0	$ (940.3)	$ (5,989.5)