Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	Apr. 28, 2013	Jan. 27, 2013
Summary of cash equivalents and marketable securities:
Amortized Cost	$ 3,191,505	$ 3,286,436
Unrealized Gain	12,278	11,670
Unrealized Loss	(905)	(843)
Estimated Fair Value	3,202,878	3,297,263
Classified as:
Cash equivalents	50,950	302,166
Marketable securities	3,151,928	2,995,097
Total cash equivalents and marketable securities	3,202,878	3,297,263
Amortized Cost
Less than one year	1,337,236	1,397,350
Due in 1-5 years	1,751,183	1,777,785
Mortgage-backed securities issued by government-sponsored enterprises not due to a single maturity date	103,086	111,301
Total	3,191,505	3,286,436
Estimated Fair Value
Less than one year	1,339,144	1,399,304
Due in 1-5 years	1,757,767	1,783,103
Mortgage-backed securities issued by government-sponsored enterprises not due to a single maturity date	105,967	114,856
Total	3,202,878	3,297,263
Debt securities of United States government agencies
Summary of cash equivalents and marketable securities:
Amortized Cost	1,007,499	867,087
Unrealized Gain	1,609	1,199
Unrealized Loss	(34)	(139)
Estimated Fair Value	1,009,074	868,147
Classified as:
Total cash equivalents and marketable securities	1,009,074	868,147
Corporate debt securities
Summary of cash equivalents and marketable securities:
Amortized Cost	1,235,850	1,255,297
Unrealized Gain	3,492	3,175
Unrealized Loss	(618)	(542)
Estimated Fair Value	1,238,724	1,257,930
Classified as:
Total cash equivalents and marketable securities	1,238,724	1,257,930
Mortgage backed securities issued by United Sates government-sponsored enterprises
Summary of cash equivalents and marketable securities:
Amortized Cost	184,927	183,034
Unrealized Gain	5,845	6,194
Unrealized Loss	(235)	(57)
Estimated Fair Value	190,537	189,171
Classified as:
Total cash equivalents and marketable securities	190,537	189,171
Money market funds
Summary of cash equivalents and marketable securities:
Amortized Cost	39,350	195,790
Unrealized Gain	0	0
Unrealized Loss	0	0
Estimated Fair Value	39,350	195,790
Classified as:
Total cash equivalents and marketable securities	39,350	195,790
Debt securities issued by United States Treasury
Summary of cash equivalents and marketable securities:
Amortized Cost	723,879	785,228
Unrealized Gain	1,332	1,102
Unrealized Loss	(18)	(105)
Estimated Fair Value	725,193	786,225
Classified as:
Total cash equivalents and marketable securities	$ 725,193	$ 786,225