Fair Value of Cash Equivalents and Marketable Securities (Details) (USD $)	Jan. 26, 2014		Jan. 27, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	$ 4,092,648,000		$ 3,297,263,000
US Government Agencies Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	1,013,327,000		868,147,000
Cash and Cash Equivalents, Fair Value Disclosure	30,000,000
Marketable Securities	983,300,000
Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	1,828,580,000		1,257,930,000
Cash and Cash Equivalents, Fair Value Disclosure	234,600,000
Marketable Securities	1,594,000,000
Mortgage backed securities issued by United Sates government-sponsored enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	188,706,000		189,171,000
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	307,865,000		195,790,000
US Treasury Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	496,453,000		786,225,000
Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	257,717,000
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	307,865,000
Fair Value, Inputs, Level 1 [Member] | US Government Agencies Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Fair Value, Inputs, Level 1 [Member] | Mortgage backed securities issued by United Sates government-sponsored enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Fair Value, Inputs, Level 1 [Member] | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	307,865,000	[1]
Fair Value, Inputs, Level 1 [Member] | US Treasury Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Fair Value, Inputs, Level 1 [Member] | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	3,784,783,000
Fair Value, Inputs, Level 2 [Member] | US Government Agencies Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	1,013,327,000	[2]
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	1,828,580,000	[3]
Fair Value, Inputs, Level 2 [Member] | Mortgage backed securities issued by United Sates government-sponsored enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	188,706,000	[4]
Fair Value, Inputs, Level 2 [Member] | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	0
Fair Value, Inputs, Level 2 [Member] | US Treasury Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	496,453,000	[4]
Fair Value, Inputs, Level 2 [Member] | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	$ 257,717,000	[4]

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

[2] Includes $30.0 million in Cash Equivalents and $983.3 million in Marketable Securities on the Consolidated Balance Sheet.

[3] Includes $234.6 million in Cash Equivalents and $1,594.0 million in Marketable Securities on the Consolidated Balance Sheet.

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