Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Details) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Offsetting Assets [Line Items]
Gross recognized assets, total derivatives subject to a master netting arrangement	$ 2,042,100,000	$ 1,864,500,000
Gross amounts offset, total derivatives subject to a master netting arrangement	1,677,800,000	1,600,200,000
Net amounts presented, total derivatives subject to a master netting arrangements	364,300,000	264,300,000
Net amount, total derivatives not subject to a master netting arrangement	364,300,000	264,300,000
Total Derivatives Not Subject to a Master Netting Arrangement	(623,600,000)	(987,400,000)
Gross recognized assets, total derivatives	2,665,700,000	2,851,900,000
Net Amount	987,900,000	1,251,700,000
Gross recognized assets, securities purchased under agreement to resell	2,050,900,000	1,600,000,000
Net amounts presented, securities purchased under agreements to resell	2,050,900,000	1,600,000,000
Gross amounts not offset, securities purchased under agreements to resell	2,050,900,000	1,600,000,000
Other assets excluding derivatives and non financial instruments	3,200,000,000	3,200,000,000
Federal funds sold	15,100,000	14,200,000
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	1,704,800,000	1,636,000,000
Gross amounts offset, total derivatives subject to a master netting arrangement	1,146,400,000	1,194,300,000
Net amounts presented, total derivatives subject to a master netting arrangements	558,400,000	441,700,000
Net amount, total derivatives not subject to a master netting arrangement	558,400,000	441,700,000
Interest Rate Swap Contracts | Over the Counter Derivative
Offsetting Assets [Line Items]
Gross recognized assets, total derivatives subject to a master netting arrangement	224,300,000	170,300,000
Gross amounts offset, total derivatives subject to a master netting arrangement	14,900,000	21,500,000
Net amounts presented, total derivatives subject to a master netting arrangements	209,400,000	148,800,000
Net amount, total derivatives not subject to a master netting arrangement	209,400,000	148,800,000
Interest Rate Swap Contracts | Exchange Cleared
Offsetting Assets [Line Items]
Gross recognized assets, total derivatives subject to a master netting arrangement	113,000,000	58,200,000
Gross amounts offset, total derivatives subject to a master netting arrangement	109,700,000	38,100,000
Net amounts presented, total derivatives subject to a master netting arrangements	3,300,000	20,100,000
Net amount, total derivatives not subject to a master netting arrangement	3,300,000	20,100,000
Cross Product Netting Adjustment
Offsetting Assets [Line Items]
Gross amounts offset, total derivatives subject to a master netting arrangement	67,800,000	23,500,000
Cross Product Collateral Adjustment
Offsetting Assets [Line Items]
Gross amounts offset, total derivatives subject to a master netting arrangement	$ 339,000,000	$ 322,800,000