Derivative Financial Instruments Schedule of Notional Amounts (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Foreign exchange contracts	$ 8,705.0	$ 9,038.1
Swaps
Derivative [Line Items]
Foreign exchange contracts	330.4	515.4
Futures, forwards and spot
Derivative [Line Items]
Foreign exchange contracts	2,905.7	3,274.5
Written options
Derivative [Line Items]
Foreign exchange contracts	3,033.1	2,934.2
Purchased options
Derivative [Line Items]
Foreign exchange contracts	$ 2,435.8	$ 2,314.1