Assets and Liabilities Measured at Fair Value on Recurring Basis Segregated by Fair Value Hierarchy Level (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	$ 32,317.9	$ 29,558.5
Trading Account	1.2	4.7
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	26,100.0	25,000.0
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Available for Sale and Trading Securities	32,319.1	29,563.2
Fair Value, Measurements, Recurring | Securities Investment
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	32,317.9	29,558.5
Trading Account	1.2	4.7
Fair Value, Measurements, Recurring | Securities Investment | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	6,178.3	4,506.9
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	36.4	4.6
Fair Value, Measurements, Recurring | Securities Investment | U.S. Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	16,366.8	16,389.2
Fair Value, Measurements, Recurring | Securities Investment | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	309.5	310.4
Fair Value, Measurements, Recurring | Securities Investment | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	3,712.2	3,577.7
Fair Value, Measurements, Recurring | Securities Investment | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	1,870.2	1,907.5
Fair Value, Measurements, Recurring | Securities Investment | Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	859.4	360.6
Fair Value, Measurements, Recurring | Securities Investment | Residential Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale		6.4
Fair Value, Measurements, Recurring | Securities Investment | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,500.1	2,321.3
Fair Value, Measurements, Recurring | Securities Investment | Auction Rate Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	17.1	18.1
Fair Value, Measurements, Recurring | Securities Investment | Commercial Mortgage Backed Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	374.4
Fair Value, Measurements, Recurring | Securities Investment | Others
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	93.5	155.8
Fair Value, Measurements, Recurring | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	1,251.7	2,250.4
Fair Value, Measurements, Recurring | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	2,623.4	4,275.2
Fair Value, Measurements, Recurring | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	228.5
Fair Value, Measurements, Recurring | Other Assets | Interest Rate Swaps
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets		232.3
Fair Value, Measurements, Recurring | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	943.9	1,054.0
Fair Value, Measurements, Recurring | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	2,519.4	4,095.5
Fair Value, Measurements, Recurring | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	131.2
Fair Value, Measurements, Recurring | Other Liabilities | Interest Rate Swaps
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities		131.8
Fair Value, Measurements, Recurring | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	10.9
Fair Value, Measurements, Recurring | Subject to master netting arrangement or similar arrangement | Derivative Financial Instruments, Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Reduction in derivatives due to cash collateral received from and deposited with derivative counterparties	322.8	315.8
Fair Value, Measurements, Recurring | Subject to master netting arrangement or similar arrangement | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	(1,600.2)	(2,257.1)
Fair Value, Measurements, Recurring | Subject to master netting arrangement or similar arrangement | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	(1,717.6)	(3,173.3)
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	6,178.3	4,506.9
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	6,178.3	4,506.9
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Securities Investment | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	6,178.3	4,506.9
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	26,123.7	25,038.2
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	26,122.5	25,033.5
Trading Account	1.2	4.7
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	36.4	4.6
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | U.S. Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	16,366.8	16,389.2
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	309.5	310.4
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	3,712.2	3,577.7
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	1,870.2	1,907.5
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	859.4	360.6
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Residential Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale		6.4
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	2,500.1	2,321.3
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Commercial Mortgage Backed Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	374.4
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Others
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	93.5	155.8
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	2,851.9	4,507.5
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 Assets	2,623.4	4,275.2
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 Assets	228.5
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Assets | Interest Rate Swaps
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets		232.3
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	2,650.7	4,227.3
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 Liabilities	2,519.4	4,095.5
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 Liabilities	131.2
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Liabilities | Interest Rate Swaps
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities		131.8
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 Liabilities	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	17.1	18.1
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	17.1	18.1
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Securities Investment | Auction Rate Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	17.1	18.1
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	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 Liabilities	10.8
Derivative Financial Instruments, Liabilities | Fair Value, Measurements, Recurring | Subject to master netting arrangement or similar arrangement
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Reduction in derivatives due to cash collateral received from and deposited with derivative counterparties	$ 440.3	$ 1,200.0