Segment and Geographic Information - Total Revenues by Geographic Location (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Revenues	$ 6,078.8	$ 7,118.3	$ 6,507.0	$ 7,918.6	$ 12,382.5	$ 5,505.9	$ 5,460.8	$ 6,074.4	$ 27,622.7	$ 29,423.6	$ 14,754.9
Gross Profit	243.2	$ 259.8	$ 260.2	$ 212.6	205.1	$ 197.6	$ 195.8	$ 185.5	975.8	784.0	671.0
Long-Lived Assets	42.4				38.7				42.4	38.7	29.4
UNITED STATES
Revenues									1,587.6	1,168.0	817.1
Gross Profit									695.3	529.4	457.0
Long-Lived Assets	33.0				29.7				33.0	29.7	23.3
Europe [Member]
Revenues									189.6	166.9	463.5
Gross Profit									189.0	166.9	120.2
Long-Lived Assets	6.8				7.3				6.8	7.3	4.8
South America [Member]
Revenues									59.5	53.9	64.8
Gross Profit									58.0	54.0	64.8
Long-Lived Assets	1.4				1.5				1.4	1.5	1.2
Asia [Member]
Revenues									25,781.4	28,030.3	13,405.1
Gross Profit									28.9	29.2	24.6
Long-Lived Assets	$ 1.2				$ 0.2				1.2	0.2	0.1
Other (geographic location) [Member]
Revenues									4.6	4.5	4.4
Gross Profit									$ 4.6	$ 4.5	$ 4.4