v3.25.1
Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($)
shares in Millions, $ in Millions
 3 Months Ended 6 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Mar. 31, 2025
Mar. 31, 2024
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Balance at beginning of period $ 3,556.0 $ 3,787.0 $ 3,675.0 $ 3,743.0
Other comprehensive income (loss) before reclassifications 38.0 (32.0) (67.0) 34.0
Amounts reclassified from accumulated other comprehensive loss 1.0 0.0 6.0 (6.0)
Other comprehensive income (loss) 38.0 (32.0) (62.0) 28.0
Balance at end of period 3,605.0 3,722.0 $ 3,605.0 3,722.0
Share retirement     40  
Total accumulated other comprehensive loss, net of tax        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Balance at beginning of period (872.0) (730.0) $ (772.0) (790.0)
Other comprehensive income (loss) 39.0 (32.0) (61.0) 28.0
Balance at end of period (833.0) (762.0) (833.0) (762.0)
Pension and other postretirement benefit plan adjustments, net of tax        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Balance at beginning of period (426.0) (407.0) (431.0) (407.0)
Other comprehensive income (loss) before reclassifications 0.0 0.0 0.0 0.0
Amounts reclassified from accumulated other comprehensive loss 6.0 1.0 11.0 1.0
Other comprehensive income (loss) 6.0 1.0 11.0 1.0
Balance at end of period (420.0) (406.0) (420.0) (406.0)
Accumulated currency translation adjustments, net of tax        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Balance at beginning of period (426.0) (281.0) (296.0) (365.0)
Other comprehensive income (loss) before reclassifications 44.0 (46.0) (86.0) 38.0
Amounts reclassified from accumulated other comprehensive loss 0.0 2.0 0.0 2.0
Other comprehensive income (loss) 44.0 (44.0) (86.0) 40.0
Balance at end of period (382.0) (325.0) (382.0) (325.0)
Net unrealized losses on cash flow hedges, net of tax        
AOCI Attributable to Parent, Net of Tax [Roll Forward]        
Balance at beginning of period (20.0) (42.0) (45.0) (18.0)
Other comprehensive income (loss) before reclassifications (6.0) 14.0 19.0 (4.0)
Amounts reclassified from accumulated other comprehensive loss (5.0) (3.0) (5.0) (9.0)
Other comprehensive income (loss) (11.0) 11.0 14.0 (13.0)
Balance at end of period $ (31.0) $ (31.0) $ (31.0) $ (31.0)