Fair Value of Cash Equivalents and Marketable Securities (Details) (USD $)	Oct. 27, 2013		Jan. 27, 2013
Financial assets and liabilities measured at fair value:
Estimated Fair Value	$ 2,581,628,000		$ 3,297,263,000
Cash equivalents of corporate debt securities	54,100,000
Marketable securities of corporate debt securities	1,050,000,000
Estimate of Fair Value
Financial assets and liabilities measured at fair value:
Total cash equivalents and marketable securities	2,581,628,000
Quoted Price in Active Markets for Identical Assets (Level 1)
Financial assets and liabilities measured at fair value:
Money market funds	56,697,000	[1]
Total cash equivalents and marketable securities	56,697,000
Significant Other Observable Inputs (Level 2)
Financial assets and liabilities measured at fair value:
Debt securities issued by US Government agencies	726,996,000	[2]
Debt securities issued by United States Treasury	441,528,000	[2]
Corporate debt securities	1,100,931,000	[3]
Mortgage-backed securitieis issued by Government-sponsored entities	194,600,000	[2]
Money market funds	0
Total cash equivalents and marketable securities	2,524,931,000
Corporate Debt Securities [Member]
Financial assets and liabilities measured at fair value:
Estimated Fair Value	1,100,931,000		1,257,930,000
US Government Agencies Debt Securities [Member]
Financial assets and liabilities measured at fair value:
Estimated Fair Value	726,996,000		868,147,000
US Treasury Securities [Member]
Financial assets and liabilities measured at fair value:
Estimated Fair Value	441,528,000		786,225,000
Asset-backed Securities [Member]
Financial assets and liabilities measured at fair value:
Estimated Fair Value	60,876,000		0
Asset backed securities	60,876,000	[2]
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Financial assets and liabilities measured at fair value:
Estimated Fair Value	194,600,000		189,171,000
Money Market Funds [Member]
Financial assets and liabilities measured at fair value:
Estimated Fair Value	$ 56,697,000		$ 195,790,000

[1] Included in Cash Equivalents on the Condensed Consolidated Balance Sheet.

[2] Included in Marketable Securities on the Condensed Consolidated Balance Sheet.

[3] Includes $54.1 million in Cash Equivalents and $1.05 billion in Marketable Securities on the Condensed Consolidated Balance Sheet.