Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 2,806.8	$ 1,873.8	$ 2,694.1	$ 1,346.8
Other comprehensive income	179.4	1.3	184.3	88.3
Balance at end of period	2,929.9	2,128.7	2,929.9	2,128.7
Total accumulated other comprehensive loss, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(1,012.2)	(1,527.3)	(1,017.1)	(1,614.2)
Other comprehensive income (loss) before reclassifications	144.3	(32.4)	130.8	23.8
Amounts reclassified from accumulated other comprehensive loss	34.8	33.7	53.2	64.4
Other comprehensive income	179.1	1.3	184.0	88.2
Balance at end of period	(833.1)	(1,526.0)	(833.1)	(1,526.0)
Pension and other postretirement benefit plan adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(677.2)	(1,243.6)	(694.1)	(1,271.2)
Other comprehensive income (loss) before reclassifications	151.7	0.6	151.7	0.6
Amounts reclassified from accumulated other comprehensive loss	35.7	27.4	52.6	55.0
Other comprehensive income	187.4	28.0	204.3	55.6
Balance at end of period	(489.8)	(1,215.6)	(489.8)	(1,215.6)
Accumulated currency translation adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(299.6)	(242.4)	(280.1)	(311.5)
Other comprehensive income (loss) before reclassifications	(10.1)	(33.3)	(29.6)	35.8
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0	0.0	0.0
Other comprehensive income	(10.1)	(33.3)	(29.6)	35.8
Balance at end of period	(309.7)	(275.7)	(309.7)	(275.7)
Net unrealized gains (losses) on cash flow hedges, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(35.4)	(41.3)	(42.9)	(31.5)
Other comprehensive income (loss) before reclassifications	2.7	0.3	8.7	(12.6)
Amounts reclassified from accumulated other comprehensive loss	(0.9)	6.3	0.6	9.4
Other comprehensive income	1.8	6.6	9.3	(3.2)
Balance at end of period	$ (33.6)	$ (34.7)	$ (33.6)	$ (34.7)