v3.25.2
Debt - Text (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Sep. 30, 2024
Debt Instrument [Line Items]          
Line of Credit Facility, Current Borrowing Capacity $ 640.0   $ 640.0    
Line of Credit Facility, Maximum Borrowing Capacity 1,000.0   1,000.0    
Letter of Credit, Maximum Borrowing Capacity $ 100.0   $ 100.0    
Letter of Credit, Maximum Borrowing Capacity, Percentage of Revolving Credit Commitment 50.00%   50.00%    
Long-term Line of Credit $ 0.0   $ 0.0   $ 0.0
Letters of Credit Outstanding, Amount 37.2   37.2    
Line of Credit Facility, Remaining Borrowing Capacity 602.8   602.8    
Debt 872.8   872.8   706.4
Debt Repurchase Program, Authorized Amount 30.0   30.0    
Debt Repurchase Authorization Remaining 30.0   30.0    
Gain (Loss) on Repurchase of Debt Instrument 0.0 $ 0.0 (1.1) $ 0.0  
Credit Facility Maturing December 18, 2029          
Debt Instrument [Line Items]          
Line of Credit Facility, Current Borrowing Capacity 575.0   575.0    
Credit Facility Maturing October 28, 2026          
Debt Instrument [Line Items]          
Line of Credit Facility, Current Borrowing Capacity $ 65.0   $ 65.0    
Senior Notes 3.85% [Member]          
Debt Instrument [Line Items]          
Debt Instrument, Interest Rate, Stated Percentage 3.85%   3.85%    
Debt $ 70.4   $ 70.4   398.4
Debt Instrument, Face Amount $ 70.6   $ 70.6    
Debt Instrument, Frequency of Periodic Payment     semiannually    
Debt Instrument, Interest Rate, Effective Percentage 4.10%   4.10%    
Debt Instrument, Redemption Price $ 333.4   $ 333.4    
Debt Instrument, Redemption, Accrued and Unpaid Interest     4.2    
Debt Instrument, Repurchased Face Amount 400.0   400.0    
Debt Instrument, Repurchase Amount $ 329.4   $ 329.4    
Debt Instrument, Maturity Date     May 15, 2026    
Senior Notes 3.85% [Member] | Debt Instrument, Redemption, Period One          
Debt Instrument [Line Items]          
Debt Instrument, Redemption Period, End Date     May 15, 2025    
Senior Notes 5.0% [Member]          
Debt Instrument [Line Items]          
Debt Instrument, Interest Rate, Stated Percentage 5.00%   5.00%    
Debt $ 298.5   $ 298.5   298.1
Debt Instrument, Face Amount $ 300.0   $ 300.0    
Debt Instrument, Redemption Price, Percentage     100.833%    
Debt Instrument, Frequency of Periodic Payment     semiannually    
Debt Instrument, Interest Rate, Effective Percentage 5.20%   5.20%    
Debt Instrument, Maturity Date     Mar. 01, 2028    
Senior Notes 5.0% [Member] | Debt Instrument, Redemption, Period One          
Debt Instrument [Line Items]          
Debt Instrument, Redemption Period, End Date     Mar. 01, 2026    
Senior Notes 6.50%          
Debt Instrument [Line Items]          
Debt Instrument, Interest Rate, Stated Percentage 6.50%   6.50%    
Debt $ 494.0   $ 494.0   0.0
Debt Instrument, Frequency of Periodic Payment     semiannually    
Debt Instrument, Interest Rate, Effective Percentage 6.70%   6.70%    
Debt Instrument, Issued, Principal     $ 500.0    
Debt Instrument, Maturity Date     Mar. 15, 2033    
Senior Notes 6.50% | Debt Instrument, Redemption, Period One          
Debt Instrument [Line Items]          
Debt Instrument, Redemption Price, Percentage     106.50%    
Debt Instrument, Redemption Price, Maximum Percentage of Principal Amount Redeemed     40.00%    
Debt Instrument, Redemption Period, End Date     Mar. 15, 2028    
Senior Notes 6.50% | Debt Instrument, Redemption, Period Two          
Debt Instrument [Line Items]          
Debt Instrument, Redemption Price, Percentage     103.25%    
Debt Instrument, Redemption Price, Maximum Percentage of Principal Amount Redeemed     100.00%    
Debt Instrument, Redemption Period, End Date     Mar. 15, 2030    
Unsecured Debt          
Debt Instrument [Line Items]          
Debt Instrument, Interest Rate, Stated Percentage 4.00%   4.00%    
Debt $ 9.9   $ 9.9   9.9
Senior Notes [Member]          
Debt Instrument [Line Items]          
Debt Issuance Costs, Net $ 7.6   $ 7.6   $ 3.5