Short-term Investments (Gross Gains (Losses) Realized On Sales, Maturities And Other Securities Transactions Related To Investment Securities) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Investments [Abstract]
Proceeds from sales of available-for-sale investment securities	$ 246.3	$ 178.8	$ 428.1	$ 357.8
Gross gains	0.5	0.4	0.9	0.8
Gross losses	0.0	(0.1)	(0.1)	(0.1)
Net realized gains on sales of available-for-sale investment securities	$ 0.5	$ 0.3	$ 0.8	$ 0.7