Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Details) - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Other Assets (excluding Derivative Assets)	$ 3,200,000,000	$ 3,600,000,000
Federal funds sold	10,600,000	62,700,000
Cash collateral possessed that was not offset	0	0
Derivatives
Derivative [Line Items]
Gross Recognized Assets	3,101,100,000	4,507,500,000
Gross Amounts Offset	1,167,000,000	2,257,100,000
Net Amounts Presented	1,934,100,000	2,250,400,000
Net Amount (3)	1,934,100,000	2,250,400,000
Derivatives | Total Derivatives Subject to a Master Netting Arrangement
Derivative [Line Items]
Gross Recognized Assets	2,334,700,000	3,675,100,000
Gross Amounts Offset	1,167,000,000	2,257,100,000
Net Amounts Presented	1,167,700,000	1,418,000,000
Net Amount (3)	1,167,700,000	1,418,000,000
Derivatives | Total Derivatives Not Subject to a Master Netting Arrangement
Derivative [Line Items]
Gross Recognized Assets	766,400,000	832,400,000
Net Amounts Presented	766,400,000	832,400,000
Net Amount (3)	766,400,000	832,400,000
Derivatives | Foreign Exchange Contracts | Over the Counter Derivative
Derivative [Line Items]
Gross Recognized Assets	2,051,900,000	3,442,800,000
Gross Amounts Offset	1,002,100,000	1,889,800,000
Net Amounts Presented	1,049,800,000	1,553,000,000
Net Amount (3)	1,049,800,000	1,553,000,000
Derivatives | Interest Rate Swap Contracts | Over the Counter Derivative
Derivative [Line Items]
Gross Recognized Assets	206,700,000	183,900,000
Gross Amounts Offset	29,700,000	32,100,000
Net Amounts Presented	177,000,000	151,800,000
Net Amount (3)	177,000,000	151,800,000
Derivatives | Interest Rate Swap Contracts | Exchange Cleared
Derivative [Line Items]
Gross Recognized Assets	76,100,000	48,400,000
Gross Amounts Offset	51,600,000	13,100,000
Net Amounts Presented	24,500,000	35,300,000
Net Amount (3)	24,500,000	35,300,000
Derivatives | Cross Product Netting Adjustment
Derivative [Line Items]
Gross Amounts Offset	14,600,000	6,300,000
Derivatives | Cross Product Collateral Adjustment
Derivative [Line Items]
Gross Amounts Offset	69,000,000	315,800,000
Securities Purchased under Agreements to Resell
Derivative [Line Items]
Gross Recognized Assets	1,245,000,000	1,000,000,000
Net Amounts Presented	1,245,000,000	1,000,000,000
Gross Amounts Not Offset	$ (1,245,000,000)	$ (1,000,000,000)