Derivative Financial Instruments Schedule of Fair Value by Balance Sheet Location (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative assets, gross fair value	$ 88.8	$ 80.4
Cash collateral	40.1	12.5
Derivative asset, fair value, gross, net of cash collateral	48.7	67.9
Derivative liabilities, gross fair value	86.8	68.3
Cash collateral	9.9	10.9
Derivative liabilities, fair value, gross, net of cash collateral	76.9	57.4
Foreign exchange contracts	43.0	39.0
Derivative assets, net	2.9	26.5
Foreign exchange contracts	41.0	26.9
Derivative liabilities, net	31.1	16.0
Over the counter
Derivatives, Fair Value [Line Items]
Derivative assets, gross fair value	88.8	80.4
Derivative liabilities, gross fair value	86.8	68.2
Foreign exchange contracts	43.0	39.0
Foreign exchange contracts	41.0	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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