Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Details) - USD ($)	Mar. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Other Assets (excluding Derivative Assets)	$ 3,334,400,000	$ 3,212,700,000
Federal funds sold	10,000,000	14,200,000
Cash collateral possessed that was not offset	0	0
Derivatives
Derivative [Line Items]
Gross Recognized Assets	4,286,600,000	2,851,900,000
Gross Amounts Offset	2,556,500,000	1,600,200,000
Net Amounts Presented	1,730,100,000	1,251,700,000
Net Amount	1,730,100,000	1,251,700,000
Derivatives | Total Derivatives Subject to a Master Netting Arrangement
Derivative [Line Items]
Gross Recognized Assets	3,468,900,000	1,864,500,000
Gross Amounts Offset	2,556,500,000	1,600,200,000
Net Amounts Presented	912,400,000	264,300,000
Net Amount	912,400,000	264,300,000
Derivatives | Total Derivatives Not Subject to a Master Netting Arrangement
Derivative [Line Items]
Gross Recognized Assets	817,700,000	987,400,000
Net Amounts Presented	817,700,000	987,400,000
Net Amount	817,700,000	987,400,000
Securities Purchased under Agreements to Resell
Derivative [Line Items]
Gross Recognized Assets	1,755,200,000	1,600,000,000
Net Amounts Presented	1,755,200,000	1,600,000,000
Gross Amounts Not Offset	(1,755,200,000)	(1,600,000,000)
Foreign Exchange Contracts | Over the Counter Derivative
Derivative [Line Items]
Gross Recognized Assets	3,134,900,000	1,636,000,000
Gross Amounts Offset	1,523,100,000	1,194,300,000
Net Amounts Presented	1,611,800,000	441,700,000
Net Amount	1,611,800,000	441,700,000
Interest Rate Swap Contracts | Over the Counter Derivative
Derivative [Line Items]
Gross Recognized Assets	232,500,000	170,300,000
Gross Amounts Offset	22,300,000	21,500,000
Net Amounts Presented	210,200,000	148,800,000
Net Amount	210,200,000	148,800,000
Interest Rate Swap Contracts | Exchange Cleared
Derivative [Line Items]
Gross Recognized Assets	101,500,000	58,200,000
Gross Amounts Offset	96,800,000	38,100,000
Net Amounts Presented	4,700,000	20,100,000
Net Amount	4,700,000	20,100,000
Cross Product Netting Adjustment
Derivative [Line Items]
Gross Amounts Offset	42,400,000	23,500,000
Cross Product Collateral Adjustment
Derivative [Line Items]
Gross Amounts Offset	$ 871,900,000	$ 322,800,000