Segment and Geographic Information - Total Revenues by Geographic Location (Details) - USD ($)	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Total revenues	$ 11,279,600,000	$ 7,873,000,000	$ 7,192,200,000	$ 6,552,200,000	$ 6,078,800,000	$ 7,118,300,000	$ 6,507,000,000	$ 7,918,600,000	$ 32,897,000,000	$ 27,622,700,000	$ 29,423,600,000
Operating revenues	286,900,000	$ 283,400,000	$ 271,100,000	$ 264,700,000	243,200,000	$ 259,800,000	$ 260,200,000	$ 212,600,000	1,106,100,000	975,800,000	784,000,000
Long-Lived Assets	43,900,000				42,400,000				43,900,000	42,400,000	38,700,000
UNITED STATES
Total revenues									1,947,600,000	1,587,600,000	1,168,000,000
Operating revenues									799,400,000	695,300,000	529,400,000
Long-Lived Assets	33,900,000				33,000,000				33,900,000	33,000,000	29,700,000
Europe [Member]
Total revenues									280,200,000	189,600,000	166,900,000
Operating revenues									209,600,000	189,000,000	166,900,000
Long-Lived Assets	6,600,000				6,800,000				6,600,000	6,800,000	7,300,000
South America [Member]
Total revenues									56,500,000	59,500,000	53,900,000
Operating revenues									56,500,000	58,000,000	54,000,000
Long-Lived Assets	2,100,000				1,400,000				2,100,000	1,400,000	1,500,000
Asia [Member]
Total revenues									30,606,900,000	25,781,400,000	28,030,300,000
Operating revenues									34,800,000	28,900,000	29,200,000
Long-Lived Assets	1,000,000				1,200,000				1,000,000	1,200,000	200,000
Other (geographic location) [Member]
Total revenues									5,800,000	4,600,000	4,500,000
Operating revenues									5,800,000	4,600,000	4,500,000
Long-Lived Assets	$ 300,000				$ 0				$ 300,000	$ 0	$ 0