Financial Instruments (Details 3) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Investments, Debt and Equity Securities [Abstract]
Proceeds from maturities and sales	$ 888.1	$ 2,362.2	$ 4,472.6	$ 5,185.8
Realized gains	0.3	1.1	2.7	2.1
Realized losses	$ (1.2)	$ (1.1)	$ (4.4)	$ (2.7)