Marketable Securities (Details) - USD ($) $ in Millions	6 Months Ended
	Jul. 26, 2015	Jan. 25, 2015
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	$ 4,105	$ 4,413
Unrealized Gain	6	11
Unrealized Loss	(5)	(3)
Estimated Fair Value	4,106	4,421
Classified as:
Cash equivalents	36	295
Marketable securities	4,070	4,126
Total cash equivalents and marketable securities	4,106	4,421
Amortized Cost
Less than one year	1,174	1,570
Due in 1-5 years	2,812	2,720
Mortgage-backed securities issued by government-sponsored enterprises not due to a single maturity date	119	123
Total	4,105	4,413
Estimated Fair Value
Less than one year	1,174	1,571
Due in 1-5 years	2,811	2,726
Mortgage-backed securities issued by government-sponsored enterprises not due to a single maturity date	121	124
Total	4,106	4,421
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,915
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	63
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,978
Unrealized Loss Position, Aggregate Losses
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(5)
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	(5)
Net realized gain
Realized Investment Gains	3
Corporate debt securities
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	1,972	2,185
Unrealized Gain	1	2
Unrealized Loss	(3)	(1)
Estimated Fair Value	1,970	2,186
Classified as:
Total cash equivalents and marketable securities	1,970	2,186
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,098
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	40
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,138
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)
Debt securities of United States government agencies
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	893	750
Unrealized Gain	1	1
Unrealized Loss	(1)	(1)
Estimated Fair Value	893	750
Classified as:
Total cash equivalents and marketable securities	893	750
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	504
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	504
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)
Asset-backed Securities
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	489	453
Unrealized Gain	0	0
Unrealized Loss	(1)	0
Estimated Fair Value	488	453
Classified as:
Total cash equivalents and marketable securities	488	453
Unrealized Loss Position, Fair Value
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	313
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	23
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	336
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)
Debt securities issued by United States Treasury
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	385	534
Unrealized Gain	0	3
Unrealized Loss	0	0
Estimated Fair Value	385	537
Classified as:
Total cash equivalents and marketable securities	385	537
Mortgage backed securities issued by United Sates government-sponsored enterprises
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	261	274
Unrealized Gain	4	5
Unrealized Loss	0	(1)
Estimated Fair Value	265	278
Classified as:
Total cash equivalents and marketable securities	265	278
Foreign government bonds
Summary of cash equivalents and marketable securities:
Available-for-sale Securities, Amortized Cost Basis	75	85
Unrealized Gain	0	0
Unrealized Loss	0	0
Estimated Fair Value	75	85
Classified as:
Total cash equivalents and marketable securities	75	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