Investments and Fair Value Measurements-AFS Investments (Details 4) (USD $)	3 Months Ended	12 Months Ended
	Mar. 29, 2015	Dec. 28, 2014
Fixed Income Securities [Member]
Available-for-sale investments
Amortized Cost	$ 3,764,377,000	$ 4,233,395,000
Gross Unrealized Gain	10,284,000	10,106,000
Gross Unrealized Loss	(1,717,000)	(4,740,000)
Fair Value	3,772,944,000	4,238,761,000
U.S. Treasury securities [Member]
Available-for-sale investments
Amortized Cost	6,797,000	25,194,000
Gross Unrealized Gain	19,000	0
Gross Unrealized Loss	(1,000)	(32,000)
Fair Value	6,815,000	25,162,000
U.S. Government-sponsored agency securities [Member]
Available-for-sale investments
Amortized Cost	22,414,000	7,511,000
Gross Unrealized Gain	21,000	0
Gross Unrealized Loss	(11,000)	(18,000)
Fair Value	22,424,000	7,493,000
International Government Securities [Member]
Available-for-sale investments
Amortized Cost	58,032,000	82,033,000
Gross Unrealized Gain	80,000	0
Gross Unrealized Loss	(21,000)	(314,000)
Fair Value	58,091,000	81,719,000
Corporate notes and bonds [Member]
Available-for-sale investments
Amortized Cost	635,937,000	774,869,000
Gross Unrealized Gain	1,340,000	325,000
Gross Unrealized Loss	(411,000)	(2,052,000)
Fair Value	636,866,000	773,142,000
Asset-backed securities [Member]
Available-for-sale investments
Amortized Cost	138,814,000	171,221,000
Gross Unrealized Gain	84,000	42,000
Gross Unrealized Loss	(86,000)	(353,000)
Fair Value	138,812,000	170,910,000
Mortgage-backed securities [Member]
Available-for-sale investments
Amortized Cost	31,253,000	48,378,000
Gross Unrealized Gain	63,000	6,000
Gross Unrealized Loss	(108,000)	(173,000)
Fair Value	31,208,000	48,211,000
Municipal notes and bonds [Member]
Available-for-sale investments
Amortized Cost	2,871,130,000	3,124,189,000
Gross Unrealized Gain	8,677,000	9,733,000
Gross Unrealized Loss	(1,079,000)	(1,798,000)
Fair Value	$ 2,878,728,000	$ 3,132,124,000