Marketable Securities (Details) (USD $)	3 Months Ended		6 Months Ended
	Jul. 28, 2013	Jul. 29, 2012	Jul. 28, 2013	Jul. 29, 2012	Jan. 27, 2013
Summary of cash equivalents and marketable securities:
Marketable Securities, Realized Gain (Loss), Excluding Other than Temporary Impairments	$ 1,600,000	$ 200,000	$ 1,700,000	$ 300,000
Cash and Cash Equivalents, Period Increase (Decrease)	781,800,000		(141,465,000)	(168,258,000)
Amortized Cost	2,509,384,000		2,509,384,000		3,286,436,000
Unrealized Gain	7,872,000		7,872,000		11,670,000
Unrealized Loss	(1,799,000)		(1,799,000)		(843,000)
Estimated Fair Value	2,515,457,000		2,515,457,000		3,297,263,000
Classified as:
Cash equivalents	170,885,000		170,885,000		302,166,000
Marketable securities	2,344,572,000		2,344,572,000		2,995,097,000
Total cash equivalents and marketable securities	2,515,457,000		2,515,457,000		3,297,263,000
Amortized Cost
Less than one year	991,260,000		991,260,000		1,397,350,000
Due in 1-5 years	1,430,967,000		1,430,967,000		1,777,785,000
Mortgage-backed securities issued by government-sponsored enterprises not due to a single maturity date	87,157,000		87,157,000		111,301,000
Total	2,509,384,000		2,509,384,000		3,286,436,000
Estimated Fair Value
Less than one year	992,324,000		992,324,000		1,399,304,000
Due in 1-5 years	1,434,002,000		1,434,002,000		1,783,103,000
Mortgage-backed securities issued by government-sponsored enterprises not due to a single maturity date	89,131,000		89,131,000		114,856,000
Total	2,515,457,000		2,515,457,000		3,297,263,000
Accelerated Share Repurchases, Settlement (Payment) or Receipt	750,000,000		750,000,000
Debt securities of United States government agencies
Summary of cash equivalents and marketable securities:
Amortized Cost	691,223,000		691,223,000		867,087,000
Unrealized Gain	634,000		634,000		1,199,000
Unrealized Loss	(393,000)		(393,000)		(139,000)
Estimated Fair Value	691,464,000		691,464,000		868,147,000
Classified as:
Total cash equivalents and marketable securities	691,464,000		691,464,000		868,147,000
Corporate debt securities
Summary of cash equivalents and marketable securities:
Amortized Cost	965,222,000		965,222,000		1,255,297,000
Unrealized Gain	1,637,000		1,637,000		3,175,000
Unrealized Loss	(914,000)		(914,000)		(542,000)
Estimated Fair Value	965,945,000		965,945,000		1,257,930,000
Classified as:
Total cash equivalents and marketable securities	965,945,000		965,945,000		1,257,930,000
Mortgage backed securities issued by United Sates government-sponsored enterprises
Summary of cash equivalents and marketable securities:
Amortized Cost	191,265,000		191,265,000		183,034,000
Unrealized Gain	5,114,000		5,114,000		6,194,000
Unrealized Loss	(362,000)		(362,000)		(57,000)
Estimated Fair Value	196,017,000		196,017,000		189,171,000
Classified as:
Total cash equivalents and marketable securities	196,017,000		196,017,000		189,171,000
Money market funds
Summary of cash equivalents and marketable securities:
Amortized Cost	164,885,000		164,885,000		195,790,000
Unrealized Gain	0		0		0
Unrealized Loss	0		0		0
Estimated Fair Value	164,885,000		164,885,000		195,790,000
Classified as:
Total cash equivalents and marketable securities	164,885,000		164,885,000		195,790,000
Debt securities issued by United States Treasury
Summary of cash equivalents and marketable securities:
Amortized Cost	496,789,000		496,789,000		785,228,000
Unrealized Gain	487,000		487,000		1,102,000
Unrealized Loss	(130,000)		(130,000)		(105,000)
Estimated Fair Value	497,146,000		497,146,000		786,225,000
Classified as:
Total cash equivalents and marketable securities	$ 497,146,000		$ 497,146,000		$ 786,225,000