Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Details) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Offsetting Assets [Line Items]
Gross recognized assets, total derivatives subject to a master netting arrangement	$ 2,602,800,000	$ 3,047,600,000
Gross amounts offset, total derivatives subject to a master netting arrangement	2,131,700,000	2,170,400,000
Net amounts presented, total derivatives subject to a master netting arrangements	471,100,000	877,200,000
Net amount, total derivatives not subject to a master netting arrangement	471,100,000	877,200,000
Total Derivatives Not Subject to a Master Netting Arrangement	(594,200,000)	(809,200,000)
Gross recognized assets, total derivatives	3,197,000,000	3,856,800,000
Net Amount	1,065,300,000	1,686,400,000
Gross recognized assets, securities purchased under agreement to resell	2,087,000,000	1,967,500,000
Net amounts presented, securities purchased under agreements to resell	2,087,000,000	1,967,500,000
Gross amounts not offset, securities purchased under agreements to resell	2,087,000,000	1,967,500,000
Other assets excluding derivatives and non financial instruments	3,400,000,000	3,300,000,000
Federal funds sold	10,000,000	6,800,000
Cash collateral possessed that was not offset	0	0
Foreign Exchange Contracts | Over the Counter Derivative
Offsetting Assets [Line Items]
Gross recognized assets, total derivatives subject to a master netting arrangement	2,480,400,000	2,800,400,000
Gross amounts offset, total derivatives subject to a master netting arrangement	1,493,100,000	1,651,900,000
Net amounts presented, total derivatives subject to a master netting arrangements	987,300,000	1,148,500,000
Net amount, total derivatives not subject to a master netting arrangement	987,300,000	1,148,500,000
Interest Rate Swap Contracts | Over the Counter Derivative
Offsetting Assets [Line Items]
Gross recognized assets, total derivatives subject to a master netting arrangement	17,700,000	129,800,000
Gross amounts offset, total derivatives subject to a master netting arrangement	12,100,000	18,200,000
Net amounts presented, total derivatives subject to a master netting arrangements	5,600,000	111,600,000
Net amount, total derivatives not subject to a master netting arrangement	5,600,000	111,600,000
Interest Rate Swap Contracts | Exchange Cleared
Offsetting Assets [Line Items]
Gross recognized assets, total derivatives subject to a master netting arrangement	104,700,000	117,400,000
Gross amounts offset, total derivatives subject to a master netting arrangement	27,100,000	21,800,000
Net amounts presented, total derivatives subject to a master netting arrangements	77,600,000	95,600,000
Net amount, total derivatives not subject to a master netting arrangement	77,600,000	95,600,000
Cross Product Netting Adjustment
Offsetting Assets [Line Items]
Gross amounts offset, total derivatives subject to a master netting arrangement	15,600,000	17,200,000
Cross Product Collateral Adjustment
Offsetting Assets [Line Items]
Gross amounts offset, total derivatives subject to a master netting arrangement	$ 583,800,000	$ 461,300,000