v3.25.2
Securities (Securities with Unrealized Losses) (Details)
$ in Millions
Jun. 30, 2025
USD ($)
security
Dec. 31, 2024
USD ($)
security
FAIR VALUE    
LESS THAN 12 MONTHS $ 9,153.3 $ 8,748.5
12 MONTHS OR LONGER 8,770.2 9,083.7
TOTAL 17,923.5 17,832.2
UNREALIZED LOSSES    
LESS THAN 12 MONTHS 20.0 28.3
12 MONTHS OR LONGER 175.6 226.8
TOTAL 195.6 255.1
U.S. Government    
FAIR VALUE    
LESS THAN 12 MONTHS 4,757.3 4,477.5
12 MONTHS OR LONGER 843.1 532.3
TOTAL 5,600.4 5,009.8
UNREALIZED LOSSES    
LESS THAN 12 MONTHS 5.5 11.1
12 MONTHS OR LONGER 8.8 11.8
TOTAL 14.3 22.9
Obligations of States and Political Subdivisions    
FAIR VALUE    
LESS THAN 12 MONTHS 0.0 0.0
12 MONTHS OR LONGER 306.8 297.5
TOTAL 306.8 297.5
UNREALIZED LOSSES    
LESS THAN 12 MONTHS 0.0 0.0
12 MONTHS OR LONGER 14.0 13.6
TOTAL 14.0 13.6
Government Sponsored Agency    
FAIR VALUE    
LESS THAN 12 MONTHS 4,068.7 3,298.8
12 MONTHS OR LONGER 5,957.7 6,373.8
TOTAL 10,026.4 9,672.6
UNREALIZED LOSSES    
LESS THAN 12 MONTHS 14.0 14.5
12 MONTHS OR LONGER 99.1 118.0
TOTAL 113.1 132.5
Non-U.S. Government    
FAIR VALUE    
LESS THAN 12 MONTHS 0.0 54.9
12 MONTHS OR LONGER 193.6 181.6
TOTAL 193.6 236.5
UNREALIZED LOSSES    
LESS THAN 12 MONTHS 0.0 0.1
12 MONTHS OR LONGER 7.9 12.2
TOTAL 7.9 12.3
Corporate Debt    
FAIR VALUE    
LESS THAN 12 MONTHS 0.0 0.0
12 MONTHS OR LONGER 42.6 76.9
TOTAL 42.6 76.9
UNREALIZED LOSSES    
LESS THAN 12 MONTHS 0.0 0.0
12 MONTHS OR LONGER 0.5 1.6
TOTAL $ 0.5 $ 1.6
Number of debt securities, available-for-sale | security 1 1
Debt securities, available-for-sale, continuous unrealized loss position with credit loss $ 41.7 $ 38.9
Debt securities, available-for-sale, continuous unrealized loss position, accumulated loss, with credit loss 0.6 1.3
Allowance for credit losses for AFS securities 0.9 0.2
Covered Bonds    
FAIR VALUE    
LESS THAN 12 MONTHS 0.0 0.0
12 MONTHS OR LONGER 123.9 119.6
TOTAL 123.9 119.6
UNREALIZED LOSSES    
LESS THAN 12 MONTHS 0.0 0.0
12 MONTHS OR LONGER 2.2 3.6
TOTAL 2.2 3.6
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds    
FAIR VALUE    
LESS THAN 12 MONTHS 250.7 881.9
12 MONTHS OR LONGER 754.5 720.5
TOTAL 1,005.2 1,602.4
UNREALIZED LOSSES    
LESS THAN 12 MONTHS 0.5 2.6
12 MONTHS OR LONGER 26.3 39.6
TOTAL $ 26.8 42.2
Number of debt securities, available-for-sale | security 1  
Debt securities, available-for-sale, continuous unrealized loss position with credit loss $ 31.9  
Debt securities, available-for-sale, continuous unrealized loss position, accumulated loss, with credit loss 0.7  
Other Asset-Backed    
FAIR VALUE    
LESS THAN 12 MONTHS 19.8 35.4
12 MONTHS OR LONGER 285.6 405.4
TOTAL 305.4 440.8
UNREALIZED LOSSES    
LESS THAN 12 MONTHS 0.0 0.0
12 MONTHS OR LONGER 6.9 12.9
TOTAL 6.9 12.9
Commercial Mortgage-Backed    
FAIR VALUE    
LESS THAN 12 MONTHS 56.8 0.0
12 MONTHS OR LONGER 262.4 376.1
TOTAL 319.2 376.1
UNREALIZED LOSSES    
LESS THAN 12 MONTHS 0.0 0.0
12 MONTHS OR LONGER 9.9 13.5
TOTAL $ 9.9 $ 13.5