Derivative Financial Instruments Schedule of Fair Value by Balance Sheet Location (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative assets, gross fair value	$ 103.8	$ 80.4
Cash collateral	11.0	12.5
Derivative asset, fair value, gross, net of cash collateral	92.8	67.9
Derivative liabilities, gross fair value	89.9	68.3
Cash collateral	10.6	10.9
Derivative liabilities, fair value, gross, net of cash collateral	79.3	57.4
Foreign exchange contracts	37.8	39.0
Derivative assets, net	26.8	26.5
Foreign exchange contracts	23.9	26.9
Derivative liabilities, net	13.3	16.0
Over the counter
Derivatives, Fair Value [Line Items]
Derivative assets, gross fair value	103.8	80.4
Derivative liabilities, gross fair value	89.9	68.2
Foreign exchange contracts	37.8	39.0
Foreign exchange contracts	23.9	26.8
Exchange traded
Derivatives, Fair Value [Line Items]
Derivative assets, gross fair value	0.0	0.0
Derivative liabilities, gross fair value	0.0	0.1
Foreign exchange contracts	0.0	0.0
Foreign exchange contracts	$ 0.0	$ 0.1