Equity (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Components of accumulated other comprehensive income (loss)
Balance at beginning of period			$ 256.8
Net current period other comprehensive income (loss)	24.4	(33.9)	58.3	13.7
Balance at end of the period	315.1		315.1
Unrealized Gain on Available-for-Sale Securities
Components of accumulated other comprehensive income (loss)
Balance at beginning of period			253.7
Net current period other comprehensive income (loss)			63.0
Balance at end of the period	316.7		316.7
Unrealized Loss on Cash Flow Hedges
Components of accumulated other comprehensive income (loss)
Balance at beginning of period			(1.4)
Net current period other comprehensive income (loss)			0.7
Balance at end of the period	(0.7)		(0.7)
Foreign Currency Translation Adjustments
Components of accumulated other comprehensive income (loss)
Balance at beginning of period			4.5
Net current period other comprehensive income (loss)			(5.4)
Balance at end of the period	$ (0.9)		$ (0.9)