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

12 Months Ended

Dec. 31, 2015

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 December 31, 2015 and 2014 were as follows:

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

December 31, 2014	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Estimated Fair Value
U.S. Treasury securities	$	1,044.7	$	0.3	$	(0.8	)	$	1,044.2
U.S. government-sponsored agency securities	145.1		0.1		(0.1		)	145.1
U.S. government-sponsored agency MBS	531.1		1.0		(2.7		)	529.4
Non-U.S. government, agency and supranational securities	32.4		—		(0.1		)	32.3
Corporate debt – global	446.3		0.6		(1.2		)	445.7
Asset backed securities	177.3		—		(0.2		)	177.1
Marketable equity securities	335.2		716.3		(0.2		)	1,051.3
Total available-for-sale marketable securities	$	2,712.1	$	718.3	$	(5.3	)	$	3,425.1

Schedule of available-for-sale securities in an unrealized loss position for less than and longer than 12 months

The fair value of all available-for-sale securities, which have been in an unrealized loss position for less than and longer than 12 months at December 31, 2015, was as follows:

	Less than 12 months					12 months or longer					Total
December 31, 2015	Estimated Fair Value		Gross Unrealized Loss			Estimated Fair Value		Gross Unrealized Loss			Estimated Fair Value		Gross Unrealized Loss
U.S. Treasury securities	$	143.6	$	(0.4	)	$	—	$	—		$	143.6	$	(0.4	)
U.S. government-sponsored agency MBS	12.8		(0.3		)	6.8		(0.1		)	19.6		(0.4		)
Corporate debt – global	193.5		(1.6		)	—		—			193.5		(1.6		)
Asset backed securities	29.6		(0.1		)	5.9		—			35.5		(0.1		)
Marketable equity securities	494.4		(43.7		)	—		—			494.4		(43.7		)
Total	$	873.9	$	(46.1	)	$	12.7	$	(0.1	)	$	886.6	$	(46.2	)

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

Duration periods of available-for-sale debt securities at December 31, 2015 were as follows:

	Amortized Cost		Fair Value
Duration of one year or less	$	58.4	$	58.3
Duration of one through three years	363.7		361.8
Duration of three through five years	15.9		15.6
Total	$	438.0	$	435.7