v3.25.2
Securities (Credit Quality Indicators) (Details)
$ in Millions
Jun. 30, 2025
USD ($)
Dec. 31, 2024
USD ($)
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities $ 21,400.8 $ 22,296.7
Percentage of debt securities, held-to-maturity, portfolio 1 1
AAA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities $ 15,374.7 $ 15,780.9
Percentage of debt securities, held-to-maturity, portfolio 0.72 0.71
AA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities $ 3,730.2 $ 3,404.1
Percentage of debt securities, held-to-maturity, portfolio 0.17 0.15
A    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities $ 1,325.8 $ 2,208.7
Percentage of debt securities, held-to-maturity, portfolio 0.06 0.10
BBB    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities $ 365.7 $ 312.6
Percentage of debt securities, held-to-maturity, portfolio 0.02 0.01
NOT RATED    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities $ 604.4 $ 590.4
Percentage of debt securities, held-to-maturity, portfolio 0.03 0.03
Obligations of States and Political Subdivisions    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities $ 2,529.0 $ 2,548.2
Obligations of States and Political Subdivisions | AAA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 1,016.4 1,024.3
Obligations of States and Political Subdivisions | AA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 1,512.6 1,523.9
Obligations of States and Political Subdivisions | A    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Obligations of States and Political Subdivisions | BBB    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Obligations of States and Political Subdivisions | NOT RATED    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Government Sponsored Agency    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 8,443.5 8,635.0
Government Sponsored Agency | AAA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 8,443.5 8,635.0
Government Sponsored Agency | AA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Government Sponsored Agency | A    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Government Sponsored Agency | BBB    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Government Sponsored Agency | NOT RATED    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Non-U.S. Government    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 2,876.4 3,735.8
Non-U.S. Government | AAA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 356.5 700.0
Non-U.S. Government | AA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 965.4 704.2
Non-U.S. Government | A    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 1,190.0 2,020.1
Non-U.S. Government | BBB    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 364.5 311.5
Non-U.S. Government | NOT RATED    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Corporate Debt    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 297.5 351.6
Corporate Debt | AAA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Corporate Debt | AA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 193.7 191.5
Corporate Debt | A    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 103.8 160.1
Corporate Debt | BBB    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Corporate Debt | NOT RATED    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Covered Bonds    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 1,541.7 1,776.8
Covered Bonds | AAA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 1,541.7 1,776.8
Covered Bonds | AA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Covered Bonds | A    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Covered Bonds | BBB    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Covered Bonds | NOT RATED    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Certificates of Deposit    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 536.2 336.0
Certificates of Deposit | AAA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 503.2 316.6
Certificates of Deposit | AA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Certificates of Deposit | A    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Certificates of Deposit | BBB    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Certificates of Deposit | NOT RATED    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 33.0 19.4
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 4,512.8 4,146.9
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | AAA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 3,458.7 3,132.8
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | AA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 1,020.9 984.5
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | A    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 32.0 28.5
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | BBB    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 1.2 1.1
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | NOT RATED    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Other Asset-Backed    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities   107.1
Other Asset-Backed | AAA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities   107.1
Other Asset-Backed | AA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities   0.0
Other Asset-Backed | A    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities   0.0
Other Asset-Backed | BBB    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities   0.0
Other Asset-Backed | NOT RATED    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities   0.0
Commercial Mortgage-Backed    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 37.6 37.6
Commercial Mortgage-Backed | AAA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 37.6
Commercial Mortgage-Backed | AA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 37.6 0.0
Commercial Mortgage-Backed | A    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Commercial Mortgage-Backed | BBB    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Commercial Mortgage-Backed | NOT RATED    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Other securities [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 626.1 621.7
Other securities [Member] | AAA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 54.7 50.7
Other securities [Member] | AA    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Other securities [Member] | A    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Other securities [Member] | BBB    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities 0.0 0.0
Other securities [Member] | NOT RATED    
Schedule of Held-to-maturity Securities [Line Items]    
Held to maturity securities $ 571.4 $ 571.0