Derivative Financial Instruments Schedule of Fair Value by Balance Sheet Location (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative assets, gross fair value	$ 75.3	$ 80.4
Cash collateral	26.5	12.5
Derivative asset, fair value, gross, net of cash collateral	48.8	67.9
Derivative liabilities, gross fair value	75.6	68.3
Cash collateral	12.3	10.9
Derivative liabilities, fair value, gross, net of cash collateral	63.3	57.4
Foreign exchange contracts	28.3	39.0
Derivative assets, net	1.8	26.5
Foreign exchange contracts	28.6	26.9
Derivative liabilities, net	16.3	16.0
Over the counter
Derivatives, Fair Value [Line Items]
Derivative assets, gross fair value	75.3	80.4
Derivative liabilities, gross fair value	75.6	68.2
Foreign exchange contracts	28.3	39.0
Foreign exchange contracts	28.6	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

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