Cash, Cash Equivalents and Marketable Securities Available-for-Sale (Tables)

3 Months Ended

Mar. 31, 2016

Cash, Cash Equivalents, and Short-term Investments [Abstract]

Schedule of available-for-sale securities by major security type and class

The amortized cost, gross unrealized holding gains, gross unrealized holding losses and estimated fair value of available-for-sale securities by major security type and class of security at March 31, 2016 and December 31, 2015 were as follows:

March 31, 2016	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Estimated Fair Value
U.S. Treasury securities	$	129.6	$	0.3	$	—		$	129.9
U.S. government-sponsored agency MBS	19.6		0.1		(0.1		)	19.6
Corporate debt - global	161.5		0.6		(0.2		)	161.9
Asset backed securities	25.4		—		—			25.4
Marketable equity securities	875.1		171.5		(121.6		)	925.0
Total available-for-sale marketable securities	$	1,211.2	$	172.5	$	(121.9	)	$	1,261.8

December 31, 2015	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Estimated Fair Value
U.S. Treasury securities	$	153.0	$	—	$	(0.4	)	$	152.6
U.S. government-sponsored agency MBS	29.8		0.1		(0.4		)	29.5
Corporate debt - global	219.7		—		(1.6		)	218.1
Asset backed securities	35.6		—		(0.1		)	35.5
Marketable equity securities	811.5		468.1		(43.7		)	1,235.9
Total available-for-sale marketable securities	$	1,249.6	$	468.2	$	(46.2	)	$	1,671.6

Schedule of duration periods of available-for-sale debt securities

Duration periods of available-for-sale debt securities at March 31, 2016 were as follows:

	Amortized Cost		Fair Value
Duration of one year or less	$	38.1	$	38.0
Duration of one through three years	287.7		288.4
Duration of three through five years	10.3		10.4
Total	$	336.1	$	336.8