Equity (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Components of accumulated other comprehensive income (loss)
Balance at beginning of period	$ 308.2
Net current period other comprehensive income (loss)	(40.8)	33.9
Balance at end of the period	267.4
Unrealized Gain on Available-for-Sale Securities
Components of accumulated other comprehensive income (loss)
Balance at beginning of period	300.8
Net current period other comprehensive income (loss)	(41.4)
Balance at end of the period	259.4
Unrealized Loss on Cash Flow Hedges
Components of accumulated other comprehensive income (loss)
Balance at beginning of period	(0.5)
Net current period other comprehensive income (loss)	0.2
Balance at end of the period	(0.3)
Foreign Currency Translation Adjustments
Components of accumulated other comprehensive income (loss)
Balance at beginning of period	7.9
Net current period other comprehensive income (loss)	0.4
Balance at end of the period	$ 8.3