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

6 Months Ended

Jun. 30, 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 June 30, 2016 and December 31, 2015 were as follows:

June 30, 2016	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Estimated Fair Value
U.S. Treasury securities	$	124.6	$	0.4	$	—		$	125.0
U.S. government-sponsored agency MBS	28.6		0.1		—			28.7
Corporate debt - global	163.9		1.1		(0.1		)	164.9
Asset backed securities	26.5		0.1		—			26.6
Marketable equity securities	887.2		213.6		(106.0		)	994.8
Total available-for-sale marketable securities	$	1,230.8	$	215.3	$	(106.1	)	$	1,340.0

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 June 30, 2016 were as follows:

	Amortized Cost		Fair Value
Duration of one year or less	$	41.4	$	41.4
Duration of one through three years	288.4		289.8
Duration of three through five years	13.8		14.0
Total	$	343.6	$	345.2