Derivative Financial Instruments - Schedule of Notional Amounts (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Total	$ 10,735.4	$ 9,038.2
Swaps
Derivative [Line Items]
Total	929.5	515.4
Futures, forwards and spot
Derivative [Line Items]
Total	3,249.9	3,274.5
Written options
Derivative [Line Items]
Total	3,688.8	2,934.2
Purchased options
Derivative [Line Items]
Total	$ 2,867.2	$ 2,314.1