Assets and Liabilities Measured at Fair Value on Recurring Basis Segregated by Fair Value Hierarchy Level (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	$ 35,579.8	$ 32,317.9
Trading Account	0.3	1.2
Derivative Asset, Gross	3,856.8	2,851.9
Derivative Asset	1,686.4	1,251.7
Derivative Liability, Gross	3,376.1	2,661.5
Derivative Liabilities	944.9	943.9
Gross Amounts Offset	2,170.4	1,600.2
Reduction in derivatives due to cash collateral received from and deposited with derivative counterparties	2,431.2	1,717.6
Cross Product Collateral Adjustment
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Gross Amounts Offset	461.3	322.8
Reduction in derivatives due to cash collateral received from and deposited with derivative counterparties	722.1	440.2
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	28,100.0	26,100.0
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Available for Sale and Trading Securities	35,580.1	32,319.1
Fair Value, Measurements, Recurring | Securities Investment
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	35,579.8	32,317.9
Trading Account	0.3	1.2
Fair Value, Measurements, Recurring | Securities Investment | U.S. Government Obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	7,522.6	6,178.3
Fair Value, Measurements, Recurring | Securities Investment | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	885.2	36.4
Fair Value, Measurements, Recurring | Securities Investment | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	17,892.8	16,366.8
Fair Value, Measurements, Recurring | Securities Investment | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	417.9	309.5
Fair Value, Measurements, Recurring | Securities Investment | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	3,765.2	3,712.2
Fair Value, Measurements, Recurring | Securities Investment | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	1,143.9	1,870.2
Fair Value, Measurements, Recurring | Securities Investment | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	1,340.7	859.4
Fair Value, Measurements, Recurring | Securities Investment | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,085.1	2,500.1
Fair Value, Measurements, Recurring | Securities Investment | Auction Rate
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	4.7	17.1
Fair Value, Measurements, Recurring | Securities Investment | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	471.6	374.4
Fair Value, Measurements, Recurring | Securities Investment | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	50.1	93.5
Fair Value, Measurements, Recurring | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset, Netting	(2,170.4)	(1,600.2)
Derivative Asset	1,686.4	1,251.7
Fair Value, Measurements, Recurring | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset	3,609.6	2,623.4
Fair Value, Measurements, Recurring | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset	247.2	228.5
Fair Value, Measurements, Recurring | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liability, Netting	(2,431.2)	(1,717.6)
Derivative Liabilities	944.9	943.9
Fair Value, Measurements, Recurring | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	3,242.9	2,519.4
Fair Value, Measurements, Recurring | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	108.0	131.2
Fair Value, Measurements, Recurring | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	25.2	10.9
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Available for Sale and Trading Securities	7,522.6	6,178.3
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Securities Investment
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	7,522.6	6,178.3
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Securities Investment | U.S. Government Obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	7,522.6	6,178.3
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Available for Sale and Trading Securities	28,052.8	26,123.7
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	28,052.5	26,122.5
Trading Account	0.3	1.2
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	885.2	36.4
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	17,892.8	16,366.8
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	417.9	309.5
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	3,765.2	3,712.2
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	1,143.9	1,870.2
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	1,340.7	859.4
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,085.1	2,500.1
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	471.6	374.4
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	50.1	93.5
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset, Gross	3,856.8	2,851.9
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset, Gross	3,609.6	2,623.4
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset, Gross	247.2	228.5
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liability, Gross	3,350.9	2,650.7
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liability, Gross	3,242.9	2,519.4
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liability, Gross	108.0	131.2
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liability, Gross	0.0	0.1
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Available for Sale and Trading Securities	4.7	17.1
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Securities Investment
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	4.7	17.1
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Securities Investment | Auction Rate
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	4.7	17.1
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liability, Gross	25.2	10.8
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liability, Gross	$ 25.2	$ 10.8