Marketable Securities (Details) (USD $)	3 Months Ended	6 Months Ended		12 Months Ended
	Jul. 28, 2013	Jul. 27, 2014	Jul. 28, 2013	Jan. 26, 2014
Summary of cash equivalents and marketable securities:
Realized Investment Gains (Losses)	$ 1,600,000		$ 1,700,000
Available-for-sale Securities, Amortized Cost Basis		4,118,873,000		4,087,893,000
Unrealized Gain		7,835,000		7,178,000
Unrealized Loss		(3,365,000)		(2,423,000)
Estimated Fair Value		4,123,343,000		4,092,648,000
Classified as:
Cash equivalents		252,381,000		572,425,000
Marketable securities		3,870,962,000		3,520,223,000
Total cash equivalents and marketable securities		4,123,343,000		4,092,648,000
Amortized Cost
Less than one year		1,296,254,000		1,883,132,000
Due in 1-5 years		2,665,096,000		2,114,289,000
Mortgage-backed securities issued by government-sponsored enterprises not due to a single maturity date		157,523,000		90,472,000
Total		4,118,873,000		4,087,893,000
Estimated Fair Value
Less than one year		1,296,861,000		1,883,753,000
Due in 1-5 years		2,667,222,000		2,117,387,000
Mortgage-backed securities issued by government-sponsored enterprises not due to a single maturity date		159,260,000		91,508,000
Total		4,123,343,000		4,092,648,000
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		1,177,370,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		2,826,482,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		4,003,852,000
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		(135,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		(3,230,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		(3,365,000)
Corporate debt securities
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis		2,042,721,000		1,827,788,000
Unrealized Gain		2,139,000		1,857,000
Unrealized Loss		(1,430,000)		(1,065,000)
Estimated Fair Value		2,043,430,000		1,828,580,000
Classified as:
Total cash equivalents and marketable securities		2,043,430,000		1,828,580,000
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		664,945,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		1,378,485,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		2,043,430,000
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		(90,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		(1,340,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		(1,430,000)
Debt securities of United States government agencies
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis		700,025,000		1,012,740,000
Unrealized Gain		352,000		848,000
Unrealized Loss		(216,000)		(261,000)
Estimated Fair Value		700,161,000		1,013,327,000
Classified as:
Total cash equivalents and marketable securities		700,161,000		1,013,327,000
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		304,481,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		395,680,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		700,161,000
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		(3,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		(213,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		(216,000)
Debt securities issued by United States Treasury
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis		586,484,000		495,889,000
Unrealized Gain		896,000		621,000
Unrealized Loss		(69,000)		(57,000)
Estimated Fair Value		587,311,000		496,453,000
Classified as:
Total cash equivalents and marketable securities		587,311,000		496,453,000
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		45,045,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		542,266,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		587,311,000
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		(28,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		(41,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		(69,000)
Asset-backed Securities
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis		411,669,000		258,017,000
Unrealized Gain		169,000		15,000
Unrealized Loss		(310,000)		(315,000)
Estimated Fair Value		411,528,000		257,717,000
Classified as:
Total cash equivalents and marketable securities		411,528,000		257,717,000
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		162,899,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		248,629,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		411,528,000
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		(14,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		(296,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		(310,000)
Mortgage backed securities issued by United Sates government-sponsored enterprises
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis		258,483,000		185,594,000
Unrealized Gain		4,279,000		3,837,000
Unrealized Loss		(1,340,000)		(725,000)
Estimated Fair Value		261,422,000		188,706,000
Classified as:
Total cash equivalents and marketable securities		261,422,000		188,706,000
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		261,422,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		261,422,000
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		(1,340,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		(1,340,000)
Money market funds
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis		119,491,000		307,865,000
Unrealized Gain		0		0
Unrealized Loss		0		0
Estimated Fair Value		119,491,000		307,865,000
Classified as:
Total cash equivalents and marketable securities		$ 119,491,000		$ 307,865,000