Derivatives - Fair Value of Derivatives (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value of Derivatives [Abstract]
Derivative Assets	$ 273.4	$ 365.6
Derivative Liabilities	263.0	262.3
Designated as hedges
Fair Value of Derivatives [Abstract]
Derivative Assets	11.3	55.1
Derivative Liabilities	36.1	1.2
Designated as hedges | Other assets | Interest rate fair value hedges
Fair Value of Derivatives [Abstract]
Derivative Assets	3.3	6.7
Designated as hedges | Other assets | Foreign currency cash flow hedges
Fair Value of Derivatives [Abstract]
Derivative Assets	8.0	48.4
Designated as hedges | Other liabilities | Interest rate fair value hedges
Fair Value of Derivatives [Abstract]
Derivative Liabilities	0.0	0.0
Designated as hedges | Other liabilities | Foreign currency cash flow hedges
Fair Value of Derivatives [Abstract]
Derivative Liabilities	36.1	1.2
Not designated as hedges
Fair Value of Derivatives [Abstract]
Derivative Assets	262.1	310.5
Derivative Liabilities	226.9	261.1
Not designated as hedges | Other assets | Foreign currency cash flow hedges
Fair Value of Derivatives [Abstract]
Derivative Assets	1.9	3.3
Not designated as hedges | Other liabilities | Foreign currency cash flow hedges
Fair Value of Derivatives [Abstract]
Derivative Liabilities	5.3	2.8
Not designated as hedges | Business Solutions | Other assets | Foreign currency cash flow hedges
Fair Value of Derivatives [Abstract]
Derivative Assets	260.2	307.2
Not designated as hedges | Business Solutions | Other liabilities | Foreign currency cash flow hedges
Fair Value of Derivatives [Abstract]
Derivative Liabilities	$ 221.6	$ 258.3