v3.25.4
Debt - Senior Unsecured Notes (Details) - USD ($)
$ in Millions
1 Months Ended
Jun. 30, 2025
Sep. 18, 2023
Jun. 22, 2023
May 04, 2021
Apr. 12, 2021
Apr. 30, 2021
Jan. 31, 2026
Feb. 01, 2025
Apr. 19, 2021
Jun. 22, 2018
Debt Instrument [Line Items]                    
Debt outstanding             $ 4,470.6 $ 4,063.8    
5.750% 2029 Senior Notes | Notes                    
Debt Instrument [Line Items]                    
Aggregate principal amount   $ 500.0                
Stated interest rate (as a percent)   5.75%         5.75%      
Debt term (in years)   5 years 6 months                
5.950% 2033 Senior Notes | Notes                    
Debt Instrument [Line Items]                    
Aggregate principal amount   $ 500.0                
Stated interest rate (as a percent)   5.95%         5.95%      
Debt term (in years)   10 years                
Senior Notes Due 2029 and 2033 | Notes                    
Debt Instrument [Line Items]                    
Redemption price percentage   101.00%                
Debt outstanding             $ 1,000.0      
1.650% 2026 Senior Notes | Notes                    
Debt Instrument [Line Items]                    
Aggregate principal amount         $ 500.0          
Stated interest rate (as a percent)         1.65%   1.65%      
Debt term (in years)         5 years          
2.450% 2028 Senior Notes | Notes                    
Debt Instrument [Line Items]                    
Aggregate principal amount         $ 750.0          
Stated interest rate (as a percent)         2.45%   2.45%      
Debt term (in years)         7 years          
2.950% 2031 Senior Notes | Notes                    
Debt Instrument [Line Items]                    
Aggregate principal amount         $ 750.0          
Stated interest rate (as a percent)         2.95%   2.95%      
Debt term (in years)         10 years          
Senior Notes Due 2026, 2028 and 2031 | Notes                    
Debt Instrument [Line Items]                    
Redemption price percentage         101.00%          
Debt outstanding             $ 2,000.0      
MTG Senior Notes | Notes                    
Debt Instrument [Line Items]                    
Debt outstanding                 $ 1,000.0  
MTG Senior Notes Due 2023 | Notes                    
Debt Instrument [Line Items]                    
Aggregate principal amount                   $ 500.0
Stated interest rate (as a percent)                   4.20%
Principal amount exchanged       $ 433.9            
MTG Senior Notes Due 2028 | Notes                    
Debt Instrument [Line Items]                    
Aggregate principal amount                   $ 500.0
Stated interest rate (as a percent)                   4.875%
Principal amount exchanged       $ 479.5            
MTI Senior Notes Due 2023 | Notes                    
Debt Instrument [Line Items]                    
Aggregate principal amount                 $ 500.0  
Stated interest rate (as a percent)                 4.20%  
MTI Senior Notes Due 2028 | Notes                    
Debt Instrument [Line Items]                    
Aggregate principal amount                 $ 500.0  
Stated interest rate (as a percent)                 4.875%  
MTI and MTG 2023 Notes | Notes                    
Debt Instrument [Line Items]                    
Repayments of senior notes     $ 500.0              
MTI Senior Notes | Notes                    
Debt Instrument [Line Items]                    
Redemption price percentage           101.00%        
2030 and 2035 Senior Notes | Notes                    
Debt Instrument [Line Items]                    
Redemption price percentage 101.00%                  
Debt outstanding             $ 1,000.0      
4.750% 2030 Senior Notes | Notes                    
Debt Instrument [Line Items]                    
Aggregate principal amount $ 500.0                  
Stated interest rate (as a percent) 4.75%           4.75%      
Debt term (in years) 5 years                  
5.450% 2035 Senior Notes | Notes                    
Debt Instrument [Line Items]                    
Aggregate principal amount $ 500.0                  
Stated interest rate (as a percent) 5.45%           5.45%      
Debt term (in years) 10 years