Financial Instruments (Details 3) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Investments, Debt and Equity Securities [Abstract]
Proceeds from maturities and sales	$ 1,700.2	$ 1,642.5	$ 3,584.5	$ 2,823.6
Realized gains	1.2	0.6	2.4	1.0
Realized losses	$ (1.3)	$ (1.2)	$ (3.2)	$ (1.6)