Offsetting of Derivative Assets and of Securities Purchased Under Agreements to Resell Within Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Derivatives
Derivative [Line Items]
Gross Recognized Assets	$ 2,851.9	$ 4,507.5
Gross Amounts Offset	1,600.2	2,257.1
Net Amounts Presented	1,251.7	2,250.4
Net Amount	1,251.7	2,250.4
Derivatives | Subject to Master Netting Arrangement
Derivative [Line Items]
Gross Recognized Assets	1,864.5	3,675.1
Gross Amounts Offset	1,600.2	2,257.1
Net Amounts Presented	264.3	1,418.0
Net Amount	264.3	1,418.0
Derivatives | Not Subject to Master Netting Arrangement
Derivative [Line Items]
Gross Recognized Assets	987.4	832.4
Net Amounts Presented	987.4	832.4
Net Amount	987.4	832.4
Derivatives | Foreign Exchange Contracts | Over the Counter Derivative
Derivative [Line Items]
Gross Recognized Assets	1,636.0	3,442.8
Gross Amounts Offset	1,194.3	1,889.8
Net Amounts Presented	441.7	1,553.0
Net Amount	441.7	1,553.0
Derivatives | Interest Rate Swaps | Over the Counter Derivative
Derivative [Line Items]
Gross Recognized Assets	170.3	183.9
Gross Amounts Offset	21.5	32.1
Net Amounts Presented	148.8	151.8
Net Amount	148.8	151.8
Derivatives | Interest Rate Swaps | Exchange Cleared
Derivative [Line Items]
Gross Recognized Assets	58.2	48.4
Gross Amounts Offset	38.1	13.1
Net Amounts Presented	20.1	35.3
Net Amount	20.1	35.3
Derivatives | Cross Product Netting Adjustment
Derivative [Line Items]
Gross Amounts Offset	23.5	6.3
Derivatives | Cross Product Collateral Adjustment
Derivative [Line Items]
Gross Amounts Offset	322.8	315.8
Securities Purchased under Agreements to Resell
Derivative [Line Items]
Gross Recognized Assets	1,600.0	1,000.0
Net Amounts Presented	1,600.0	1,000.0
Gross Amounts Not Offset	$ 1,600.0	$ 1,000.0