Fair Value Measurements (Recurring Basis Hierarchy Leveling) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	$ 28,311.9	$ 23,089.8
Derivative Assets	3,519.0	3,568.2
NETTING	(2,773.1)	(3,126.7)
Derivative Assets	745.9	441.5
Derivative Liabilities	3,615.8	3,649.8
NETTING	(1,819.9)	(2,205.4)
Derivative Liabilities	1,795.9	1,444.4
Cross Product Collateral Adjustment
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(2,000.0)	(2,100.0)
NETTING	(1,000.0)	(1,200.0)
U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	6,481.7	3,622.2
Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	306.0	295.8
Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	13,653.7	11,553.0
Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	327.1	264.4
Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	201.1	279.5
Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	239.7	347.1
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	3,988.1	2,899.9
Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,487.4	2,962.6
Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	627.1	865.3
LEVEL 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	21,800.0	19,500.0
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	28,311.9	23,089.8
Fair Value, Measurements, Recurring | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	6,481.7	3,622.2
Fair Value, Measurements, Recurring | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	306.0	295.8
Fair Value, Measurements, Recurring | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	13,653.7	11,553.0
Fair Value, Measurements, Recurring | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	327.1	264.4
Fair Value, Measurements, Recurring | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	201.1	279.5
Fair Value, Measurements, Recurring | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	239.7	347.1
Fair Value, Measurements, Recurring | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	3,988.1	2,899.9
Fair Value, Measurements, Recurring | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,487.4	2,962.6
Fair Value, Measurements, Recurring | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	627.1	865.3
Fair Value, Measurements, Recurring | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Equity Securities	112.8
Money Market Investment		95.0
NETTING	(2,773.1)	(3,126.7)
Derivative Assets	745.9	441.5
Fair Value, Measurements, Recurring | Other Assets | Money market investment
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Equity Securities	85.0
Fair Value, Measurements, Recurring | Other Assets | Visa Class C shares
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Equity Securities	27.8
Fair Value, Measurements, Recurring | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(2,664.5)	(2,937.2)
Derivative Assets	388.4	329.5
Fair Value, Measurements, Recurring | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(108.6)	(189.5)
Derivative Assets	357.5	112.0
Fair Value, Measurements, Recurring | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(1,819.9)	(2,205.4)
Derivative Liabilities	1,795.9	1,444.4
Fair Value, Measurements, Recurring | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(1,784.0)	(2,175.7)
Derivative Liabilities	1,299.9	1,079.5
Fair Value, Measurements, Recurring | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(9.1)	(6.0)
Derivative Liabilities	495.0	363.2
Fair Value, Measurements, Recurring | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(26.8)	(23.7)
Derivative Liabilities	1.0	1.7
Fair Value, Measurements, Recurring | LEVEL 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	6,481.7	3,622.2
Fair Value, Measurements, Recurring | LEVEL 1 | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	6,481.7	3,622.2
Fair Value, Measurements, Recurring | LEVEL 1 | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 1 | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 1 | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 1 | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 1 | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 1 | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 1 | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Equity Securities	85.0
Money Market Investment		95.0
Derivative Assets	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	21,830.2	19,467.6
Fair Value, Measurements, Recurring | LEVEL 2 | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 2 | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	306.0	295.8
Fair Value, Measurements, Recurring | LEVEL 2 | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	13,653.7	11,553.0
Fair Value, Measurements, Recurring | LEVEL 2 | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	327.1	264.4
Fair Value, Measurements, Recurring | LEVEL 2 | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	201.1	279.5
Fair Value, Measurements, Recurring | LEVEL 2 | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	239.7	347.1
Fair Value, Measurements, Recurring | LEVEL 2 | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	3,988.1	2,899.9
Fair Value, Measurements, Recurring | LEVEL 2 | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,487.4	2,962.6
Fair Value, Measurements, Recurring | LEVEL 2 | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	627.1	865.3
Fair Value, Measurements, Recurring | LEVEL 2 | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Equity Securities	27.8
Money Market Investment		0.0
Derivative Assets	3,519.0	3,568.2
Fair Value, Measurements, Recurring | LEVEL 2 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	3,052.9	3,266.7
Fair Value, Measurements, Recurring | LEVEL 2 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	466.1	301.5
Fair Value, Measurements, Recurring | LEVEL 2 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	3,588.0	3,624.4
Fair Value, Measurements, Recurring | LEVEL 2 | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	3,083.9	3,255.2
Fair Value, Measurements, Recurring | LEVEL 2 | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	504.1	369.2
Fair Value, Measurements, Recurring | LEVEL 2 | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Equity Securities	0.0
Money Market Investment		0.0
Derivative Assets	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	27.8	25.4
Fair Value, Measurements, Recurring | LEVEL 3 | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0.0	0.0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	$ 27.8	$ 25.4