Offsetting of Assets and Liabilities (Offsetting of Derivative Liabilities and Securities Sold Under Agreements to Repurchase) (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Offsetting Liabilities [Line Items]
Gross recognized liabilities, total derivatives subject to a master netting arrangement	$ 2,327,600,000	$ 2,767,600,000
Gross amounts offset, total derivatives subject to a master netting arrangement	2,089,800,000	2,431,200,000
Net amounts presented, total derivatives subject to a master netting arrangement	237,800,000	336,400,000
Net amount, total derivatives subject to a master netting arrangement	237,800,000	336,400,000
Total Derivatives Not Subject to a Master Netting Arrangement	952,800,000	608,500,000
Gross recognized liabilities, total derivatives	3,280,400,000	3,376,100,000
Derivative Liabilities	1,190,600,000	944,900,000
Gross recognized liabilities, securities sold under agreements to repurchase	523,900,000	473,700,000
Net amounts presented, securities sold under agreements to repurchase	523,900,000	473,700,000
Gross amounts not offset, securities sold under agreements to repurchase	523,900,000	473,700,000
Other liabilities	2,100,000,000	2,700,000,000
Cash collateral possessed that was not offset	0	0
Foreign Exchange Contracts | Over the Counter Derivative
Offsetting Liabilities [Line Items]
Gross recognized liabilities, total derivatives subject to a master netting arrangement	2,215,800,000	2,634,400,000
Gross amounts offset, total derivatives subject to a master netting arrangement	1,702,000,000	1,651,900,000
Net amounts presented, total derivatives subject to a master netting arrangement	513,800,000	982,500,000
Net amount, total derivatives subject to a master netting arrangement	513,800,000	982,500,000
Interest Rate Swap Contracts | Over the Counter Derivative
Offsetting Liabilities [Line Items]
Gross recognized liabilities, total derivatives subject to a master netting arrangement	62,000,000	86,200,000
Gross amounts offset, total derivatives subject to a master netting arrangement	12,400,000	18,200,000
Net amounts presented, total derivatives subject to a master netting arrangement	49,600,000	68,000,000
Net amount, total derivatives subject to a master netting arrangement	49,600,000	68,000,000
Interest Rate Swap Contracts | Exchange Cleared
Offsetting Liabilities [Line Items]
Gross recognized liabilities, total derivatives subject to a master netting arrangement	22,100,000	21,800,000
Gross amounts offset, total derivatives subject to a master netting arrangement	22,100,000	21,800,000
Other Financial Derivatives
Offsetting Liabilities [Line Items]
Gross recognized liabilities, total derivatives subject to a master netting arrangement	27,700,000	25,200,000
Net amounts presented, total derivatives subject to a master netting arrangement	27,700,000	25,200,000
Net amount, total derivatives subject to a master netting arrangement	27,700,000	25,200,000
Cross Product Netting Adjustment
Offsetting Liabilities [Line Items]
Gross amounts offset, total derivatives subject to a master netting arrangement	19,100,000	17,200,000
Cross Product Collateral Adjustment
Offsetting Liabilities [Line Items]
Gross amounts offset, total derivatives subject to a master netting arrangement	$ 334,200,000	$ 722,100,000