Derivative Financial Instruments Schedule of Notional Amounts (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Total	$ 10,225.9	$ 9,038.1
Swaps
Derivative [Line Items]
Total	324.2	515.4
Futures, forwards and spot
Derivative [Line Items]
Total	3,855.9	3,274.5
Written options
Derivative [Line Items]
Total	3,245.7	2,934.2
Purchased options
Derivative [Line Items]
Total	$ 2,800.1	$ 2,314.1