Offsetting of Derivative Liabilities and of Securities Sold Under Agreements to Repurchase Within Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Gross Recognized Liabilities	$ 2,767.6	$ 2,261.8
Reduction in derivatives due to cash collateral received from and deposited with derivative counterparties	2,431.2	1,717.6
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	336.4	544.2
Derivative Liability, Fair Value, Amount Offset Against Collateral	336.4	544.2
Derivative Liability, Not Subject to Master Netting Arrangement	608.5	399.7
Derivative Liability, Gross Recognized Liabilities	3,376.1	2,661.5
Derivative Liabilities	944.9	943.9
Securities Sold under Agreements to Repurchase, Gross	473.7	546.6
Net Amounts Presented	473.7	546.6
Gross Amounts Not Offset	(473.7)	(546.6)
Foreign Exchange Contracts | Over the Counter Derivative
Derivative [Line Items]
Gross Recognized Liabilities	2,634.4	2,119.7
Reduction in derivatives due to cash collateral received from and deposited with derivative counterparties	1,651.9	1,194.3
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	982.5	925.4
Derivative Liability, Fair Value, Amount Offset Against Collateral	982.5	925.4
Interest Rate Swaps | Over the Counter Derivative
Derivative [Line Items]
Gross Recognized Liabilities	86.2	93.1
Reduction in derivatives due to cash collateral received from and deposited with derivative counterparties	18.2	21.5
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	68.0	71.6
Derivative Liability, Fair Value, Amount Offset Against Collateral	68.0	71.6
Interest Rate Swaps | Exchange Cleared
Derivative [Line Items]
Gross Recognized Liabilities	21.8	38.1
Reduction in derivatives due to cash collateral received from and deposited with derivative counterparties	21.8	38.1
Other Financial Derivatives
Derivative [Line Items]
Gross Recognized Liabilities	25.2	10.9
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	25.2	10.9
Derivative Liability, Fair Value, Amount Offset Against Collateral	25.2	10.9
Cross Product Netting Adjustment
Derivative [Line Items]
Reduction in derivatives due to cash collateral received from and deposited with derivative counterparties	17.2	23.5
Cross Product Collateral Adjustment
Derivative [Line Items]
Reduction in derivatives due to cash collateral received from and deposited with derivative counterparties	$ 722.1	$ 440.2