Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Quarterly Financial Information (Unaudited)
Sales	$ 1,667.5	$ 1,599.2	$ 1,554.3	$ 1,490.3	$ 1,538.6	$ 1,474.0	$ 1,440.3	$ 1,426.6	$ 6,311.3	$ 5,879.5	$ 6,307.9
Gross profit	647.7	677.7	656.5	642.3	651.9	616.8	594.1	612.7	2,624.2	2,475.5	2,703.1
Income before income taxes	273.5	276.0	230.3	257.6	236.9	252.3	217.0	236.9	1,037.4	943.1	1,127.5
Net income	$ 204.6	$ 216.9	$ 189.5	$ 214.7	$ 185.2	$ 191.0	$ 168.0	$ 185.5	$ 825.7	$ 729.7	$ 827.6
Basic earnings per share:
Basic	$ 1.59	$ 1.69	$ 1.47	$ 1.67	$ 1.44	$ 1.47	$ 1.29	$ 1.41	$ 6.42	$ 5.60	$ 6.15
Diluted earnings per share:
Diluted	$ 1.57	$ 1.67	$ 1.45	$ 1.65	$ 1.43	$ 1.46	$ 1.28	$ 1.40	$ 6.35	$ 5.56	$ 6.09