Offsetting of Derivative Assets and of Securities Purchased Under Agreements to Resell Within Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Gross Recognized Assets	$ 3,047.6	$ 1,864.5
Gross Amounts Offset	2,170.4	1,600.2
Net Amounts Presented Not Subject To Master Arrangements	877.2	264.3
Net Amount Not Subject To Master Arrangements	877.2	264.3
Total Derivatives Not Subject to a Master Netting Arrangement	809.2	987.4
Total Derivatives, Gross	3,856.8	2,851.9
Derivative Asset	1,686.4	1,251.7
Securities Purchased under Agreements to Resell, Gross	1,967.5	1,600.0
Securities Purchased under Agreements to Resell	1,967.5	1,600.0
Securities Purchased Under Agreements To Resell, Gross Amounts Not Offset	1,967.5	1,600.0
Foreign Exchange Contracts | Over the Counter Derivative
Derivative [Line Items]
Gross Recognized Assets	2,800.4	1,636.0
Gross Amounts Offset	1,651.9	1,194.3
Net Amounts Presented Not Subject To Master Arrangements	1,148.5	441.7
Net Amount Not Subject To Master Arrangements	1,148.5	441.7
Interest Rate Swaps | Over the Counter Derivative
Derivative [Line Items]
Gross Recognized Assets	129.8	170.3
Gross Amounts Offset	18.2	21.5
Net Amounts Presented Not Subject To Master Arrangements	111.6	148.8
Net Amount Not Subject To Master Arrangements	111.6	148.8
Interest Rate Swaps | Exchange Cleared
Derivative [Line Items]
Gross Recognized Assets	117.4	58.2
Gross Amounts Offset	21.8	38.1
Net Amounts Presented Not Subject To Master Arrangements	95.6	20.1
Net Amount Not Subject To Master Arrangements	95.6	20.1
Cross Product Netting Adjustment
Derivative [Line Items]
Gross Amounts Offset	17.2	23.5
Cross Product Collateral Adjustment
Derivative [Line Items]
Gross Amounts Offset	$ 461.3	$ 322.8