Marketable Securities (Details) (USD $)	3 Months Ended		9 Months Ended
	Oct. 27, 2013	Oct. 28, 2012	Oct. 27, 2013	Oct. 28, 2012	Jan. 27, 2013
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	$ 2,575,489,000		$ 2,575,489,000		$ 3,286,436,000
Unrealized Gain	7,514,000		7,514,000		11,670,000
Unrealized Loss	(1,375,000)		(1,375,000)		(843,000)
Estimated Fair Value	2,581,628,000		2,581,628,000		3,297,263,000
Accelerated Share Repurchases, Settlement (Payment) or Receipt	750,000,000		750,000,000
Change in marketable securities	715,600,000		715,600,000
Classified as:
Cash equivalents	110,758,000		110,758,000		302,166,000
Marketable securities	2,470,870,000		2,470,870,000		2,995,097,000
Total cash equivalents and marketable securities	2,581,628,000		2,581,628,000		3,297,263,000
Amortized Cost
Less than one year	848,672,000		848,672,000		1,397,350,000
Due in 1-5 years	1,628,882,000		1,628,882,000		1,777,785,000
Mortgage-backed securities issued by government-sponsored enterprises not due to a single maturity date	97,935,000		97,935,000		111,301,000
Total	2,575,489,000		2,575,489,000		3,286,436,000
Estimated Fair Value
Less than one year	849,564,000		849,564,000		1,399,304,000
Due in 1-5 years	1,632,651,000		1,632,651,000		1,783,103,000
Mortgage-backed securities issued by government-sponsored enterprises not due to a single maturity date	99,413,000		99,413,000		114,856,000
Total	2,581,628,000		2,581,628,000		3,297,263,000
Available-for-sale Securities, Continuous Unrealized Loss Position
Number of investments in an unrealized loss position with a duration less than one year	7		7
Number of invetstments unrealized loss position with a duration more than one year	9		9
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	792,866,000		792,866,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,732,065,000		1,732,065,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,524,931,000		2,524,931,000
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(79,000)		(79,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(1,296,000)		(1,296,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(1,375,000)		(1,375,000)
Net realized gain
Marketable Securities, Realized Gain (Loss), Excluding Other than Temporary Impairments	100,000	100,000	1,800,000	400,000
Debt securities of United States government agencies
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	726,382,000		726,382,000		867,087,000
Unrealized Gain	798,000		798,000		1,199,000
Unrealized Loss	(184,000)		(184,000)		(139,000)
Estimated Fair Value	726,996,000		726,996,000		868,147,000
Classified as:
Total cash equivalents and marketable securities	726,996,000		726,996,000		868,147,000
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	288,163,000		288,163,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	438,833,000		438,833,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	726,996,000		726,996,000
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(5,000)		(5,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(179,000)		(179,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(184,000)		(184,000)
Corporate debt securities
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	1,099,456,000		1,099,456,000		1,255,297,000
Unrealized Gain	2,020,000		2,020,000		3,175,000
Unrealized Loss	(545,000)		(545,000)		(542,000)
Estimated Fair Value	1,100,931,000		1,100,931,000		1,257,930,000
Classified as:
Total cash equivalents and marketable securities	1,100,931,000		1,100,931,000		1,257,930,000
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	403,313,000		403,313,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	697,618,000		697,618,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,100,931,000		1,100,931,000
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(16,000)		(16,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(529,000)		(529,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(545,000)		(545,000)
Mortgage backed securities issued by United Sates government-sponsored enterprises
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	190,993,000		190,993,000		183,034,000
Unrealized Gain	4,129,000		4,129,000		6,194,000
Unrealized Loss	(522,000)		(522,000)		(57,000)
Estimated Fair Value	194,600,000		194,600,000		189,171,000
Classified as:
Total cash equivalents and marketable securities	194,600,000		194,600,000		189,171,000
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	3,460,000		3,460,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	191,140,000		191,140,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	194,600,000		194,600,000
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(522,000)		(522,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(522,000)		(522,000)
Asset-backed Securities [Member]
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	60,886,000		60,886,000		0
Unrealized Gain	6,000		6,000		0
Unrealized Loss	(16,000)		(16,000)		0
Estimated Fair Value	60,876,000		60,876,000		0
Classified as:
Total cash equivalents and marketable securities	60,876,000		60,876,000		0
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	10,709,000		10,709,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	50,167,000		50,167,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	60,876,000		60,876,000
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(16,000)		(16,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(16,000)		(16,000)
Money market funds
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	56,697,000		56,697,000		195,790,000
Unrealized Gain	0		0		0
Unrealized Loss	0		0		0
Estimated Fair Value	56,697,000		56,697,000		195,790,000
Classified as:
Total cash equivalents and marketable securities	56,697,000		56,697,000		195,790,000
Debt securities issued by United States Treasury
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	441,075,000		441,075,000		785,228,000
Unrealized Gain	561,000		561,000		1,102,000
Unrealized Loss	(108,000)		(108,000)		(105,000)
Estimated Fair Value	441,528,000		441,528,000		786,225,000
Classified as:
Total cash equivalents and marketable securities	441,528,000		441,528,000		786,225,000
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	87,221,000		87,221,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	354,307,000		354,307,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	441,528,000		441,528,000
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(42,000)		(42,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	(66,000)		(66,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	$ (108,000)		$ (108,000)