Marketable Securities (Details) - USD ($) $ in Millions	9 Months Ended
	Oct. 25, 2015	Jan. 25, 2015
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	$ 4,348	$ 4,413
Unrealized Gain	8	11
Unrealized Loss	(3)	(3)
Estimated Fair Value	4,353	4,421
Classified as:
Cash equivalents	96	295
Marketable securities	4,257	4,126
Total cash equivalents and marketable securities	4,353	4,421
Amortized Cost
Less than one year	1,453	1,570
Due in 1-5 years	2,811	2,720
Mortgage-backed securities issued by government-sponsored enterprises not due to a single maturity date	84	123
Total	4,348	4,413
Estimated Fair Value
Less than one year	1,454	1,571
Due in 1-5 years	2,815	2,726
Mortgage-backed securities issued by government-sponsored enterprises not due to a single maturity date	84	124
Total	4,353	4,421
Net realized gain
Realized Investment Gains	3
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	871
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	80
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	951
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(3)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(3)
Corporate debt securities
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	1,975	2,185
Unrealized Gain	2	2
Unrealized Loss	(2)	(1)
Estimated Fair Value	1,975	2,186
Classified as:
Cash equivalents	51	147
Total cash equivalents and marketable securities	1,975	2,186
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	798
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	54
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	852
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(2)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(2)
Debt securities of United States government agencies
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	994	750
Unrealized Gain	1	1
Unrealized Loss	0	(1)
Estimated Fair Value	995	750
Classified as:
Cash equivalents	14	15
Total cash equivalents and marketable securities	995	750
Debt securities issued by the United States Treasury
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	554	534
Unrealized Gain	1	3
Unrealized Loss	0	0
Estimated Fair Value	555	537
Classified as:
Total cash equivalents and marketable securities	555	537
Asset-backed Securities
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	472	453
Unrealized Gain	0	0
Unrealized Loss	0	0
Estimated Fair Value	472	453
Classified as:
Cash equivalents	1
Total cash equivalents and marketable securities	472	453
Mortgage backed securities issued by United Sates government-sponsored enterprises
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	240	274
Unrealized Gain	4	5
Unrealized Loss	(1)	(1)
Estimated Fair Value	243	278
Classified as:
Total cash equivalents and marketable securities	243	278
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	73
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	26
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	99
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1)
Foreign government bonds
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	83	85
Unrealized Gain	0	0
Unrealized Loss	0	0
Estimated Fair Value	83	85
Classified as:
Total cash equivalents and marketable securities	83	85
Money market funds
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	30	132
Unrealized Gain	0	0
Unrealized Loss	0	0
Estimated Fair Value	30	132
Classified as:
Total cash equivalents and marketable securities	$ 30	$ 132