Fair Value Measurements (Recurring Basis Hierarchy Leveling) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	$ 34,632.1	$ 32,317.9
Trading Account	3.1	1.2
Gross amounts offset, total derivatives subject to a master netting arrangement	(2,606.4)	(1,600.2)
Derivative liabilities	1,215.1	943.9
Gross amounts offset, total derivatives subject to a master netting arrangement	(3,778.3)	(1,717.6)
Cross Product Collateral Adjustment
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Gross amounts offset, total derivatives subject to a master netting arrangement	(205.8)	(322.8)
Gross amounts offset, total derivatives subject to a master netting arrangement	(1,377.7)	(440.2)
Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	27,700.0	26,100.0
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Available for Sale and Trading Securities	34,635.2	32,319.1
Fair Value, Measurements, Recurring | Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	34,632.1	32,317.9
Trading Account	3.1	1.2
Fair Value, Measurements, Recurring | Securities | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	6,889.3	6,178.3
Fair Value, Measurements, Recurring | Securities | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	643.6	36.4
Fair Value, Measurements, Recurring | Securities | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	17,437.0	16,366.8
Fair Value, Measurements, Recurring | Securities | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	280.7	309.5
Fair Value, Measurements, Recurring | Securities | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	4,001.4	3,712.2
Fair Value, Measurements, Recurring | Securities | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	1,376.6	1,870.2
Fair Value, Measurements, Recurring | Securities | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	1,121.5
Fair Value, Measurements, Recurring | Securities | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	2,390.6	2,500.1
Fair Value, Measurements, Recurring | Securities | Auction Rate
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	6.1	17.1
Fair Value, Measurements, Recurring | Securities | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	410.9	374.4
Fair Value, Measurements, Recurring | Securities | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	74.4	93.5
Fair Value, Measurements, Recurring | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	2,505.8	1,251.7
Gross amounts offset, total derivatives subject to a master netting arrangement	(2,606.4)	(1,600.2)
Fair Value, Measurements, Recurring | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	4,737.7	2,623.4
Fair Value, Measurements, Recurring | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	374.5	228.5
Fair Value, Measurements, Recurring | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	1,215.1	943.9
Gross amounts offset, total derivatives subject to a master netting arrangement	(3,778.3)	(1,717.6)
Fair Value, Measurements, Recurring | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	4,695.2	2,519.4
Fair Value, Measurements, Recurring | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	269.4	131.2
Fair Value, Measurements, Recurring | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	28.8	10.9
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Available for Sale and Trading Securities	6,889.3	6,178.3
Fair Value, Measurements, Recurring | Level 1 | Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	6,889.3	6,178.3
Fair Value, Measurements, Recurring | Level 1 | Securities | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	6,889.3	6,178.3
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Available for Sale and Trading Securities	27,739.8	26,123.7
Fair Value, Measurements, Recurring | Level 2 | Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	27,736.7	26,122.5
Trading Account	3.1	1.2
Fair Value, Measurements, Recurring | Level 2 | Securities | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	643.6	36.4
Fair Value, Measurements, Recurring | Level 2 | Securities | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	17,437.0	16,366.8
Fair Value, Measurements, Recurring | Level 2 | Securities | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	280.7	309.5
Fair Value, Measurements, Recurring | Level 2 | Securities | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	4,001.4	3,712.2
Fair Value, Measurements, Recurring | Level 2 | Securities | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	1,376.6	1,870.2
Fair Value, Measurements, Recurring | Level 2 | Securities | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	1,121.5	859.4
Fair Value, Measurements, Recurring | Level 2 | Securities | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	2,390.6	2,500.1
Fair Value, Measurements, Recurring | Level 2 | Securities | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	410.9	374.4
Fair Value, Measurements, Recurring | Level 2 | Securities | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	74.4	93.5
Fair Value, Measurements, Recurring | Level 2 | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	5,112.2	2,851.9
Fair Value, Measurements, Recurring | Level 2 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	4,737.7	2,623.4
Fair Value, Measurements, Recurring | Level 2 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative assets	374.5	228.5
Fair Value, Measurements, Recurring | Level 2 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	4,964.7	2,650.7
Fair Value, Measurements, Recurring | Level 2 | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	4,695.2	2,519.4
Fair Value, Measurements, Recurring | Level 2 | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	269.4	131.2
Fair Value, Measurements, Recurring | Level 2 | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	0.1	0.1
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total Available for Sale and Trading Securities	6.1	17.1
Fair Value, Measurements, Recurring | Level 3 | Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	6.1	17.1
Fair Value, Measurements, Recurring | Level 3 | Securities | Auction Rate
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value	6.1	17.1
Fair Value, Measurements, Recurring | Level 3 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	28.7	10.8
Fair Value, Measurements, Recurring | Level 3 | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative liabilities	$ 28.7	$ 10.8