Marketable Securities (Details) - USD ($) $ in Millions	6 Months Ended
	Jul. 26, 2015	Jul. 31, 2016	Jan. 31, 2016
Summary of cash equivalents and marketable securities:
Amortized Cost		$ 4,498	$ 4,672
Unrealized Gain		14	6
Unrealized Loss		(2)	(5)
Estimated Fair Value		4,510	4,673
Classified as:
Cash equivalents		57	232
Marketable securities		4,453	4,441
Total cash equivalents and marketable securities		4,510	4,673
Amortized Cost
Less than one year		1,846	1,619
Due in 1-5 years		2,591	3,019
Mortgage-backed securities issued by government-sponsored enterprises not due to a single maturity date		61	34
Total		4,498	4,672
Estimated Fair Value
Less than one year		1,847	1,619
Due in 1-5 years		2,601	3,020
Mortgage-backed securities issued by government-sponsored enterprises not due to a single maturity date		62	34
Total		4,510	4,673
Net realized gain
Realized Investment Gains	$ 3
Unrealized Loss Position, Fair Value
Unrealized Loss, Less than Twelve Months, Fair Value		317
Unrealized Loss, Twelve Months or Longer, Fair Value		129
Unrealized Loss, Fair Value, Total		446
Unrealized Loss Position, Aggregate Losses
Unrealized Loss, Less than 12 Months, Accumulated Loss		2
Unrealized Loss, 12 Months or Longer, Accumulated Loss		0
Gross Unrealized Loss, Total		2
Corporate debt securities
Summary of cash equivalents and marketable securities:
Amortized Cost		1,972	1,903
Unrealized Gain		5	1
Unrealized Loss		(1)	(3)
Estimated Fair Value		1,976	1,901
Classified as:
Cash equivalents		5	51
Total cash equivalents and marketable securities		1,976	1,901
Unrealized Loss Position, Fair Value
Unrealized Loss, Less than Twelve Months, Fair Value		263
Unrealized Loss, Twelve Months or Longer, Fair Value		98
Unrealized Loss, Fair Value, Total		361
Unrealized Loss Position, Aggregate Losses
Unrealized Loss, Less than 12 Months, Accumulated Loss		1
Unrealized Loss, 12 Months or Longer, Accumulated Loss		0
Gross Unrealized Loss, Total		1
Debt securities of United States government agencies
Summary of cash equivalents and marketable securities:
Amortized Cost		1,046	1,170
Unrealized Gain		2	1
Unrealized Loss		0	(1)
Estimated Fair Value		1,048	1,170
Classified as:
Cash equivalents		5	90
Total cash equivalents and marketable securities		1,048	1,170
Debt securities issued by the United States Treasury
Summary of cash equivalents and marketable securities:
Amortized Cost		809	800
Unrealized Gain		3	1
Unrealized Loss		0	0
Estimated Fair Value		812	801
Classified as:
Total cash equivalents and marketable securities		812	801
Asset-backed Securities
Summary of cash equivalents and marketable securities:
Amortized Cost		369	435
Unrealized Gain		1	0
Unrealized Loss		0	0
Estimated Fair Value		370	435
Classified as:
Total cash equivalents and marketable securities		370	435
Mortgage backed securities issued by United Sates government-sponsored enterprises
Summary of cash equivalents and marketable securities:
Amortized Cost		175	229
Unrealized Gain		3	3
Unrealized Loss		(1)	(1)
Estimated Fair Value		177	231
Classified as:
Total cash equivalents and marketable securities		177	231
Unrealized Loss Position, Fair Value
Unrealized Loss, Less than Twelve Months, Fair Value		54
Unrealized Loss, Twelve Months or Longer, Fair Value		31
Unrealized Loss, Fair Value, Total		85
Unrealized Loss Position, Aggregate Losses
Unrealized Loss, Less than 12 Months, Accumulated Loss		1
Unrealized Loss, 12 Months or Longer, Accumulated Loss		0
Gross Unrealized Loss, Total		1
Foreign government bonds
Summary of cash equivalents and marketable securities:
Amortized Cost		80	92
Unrealized Gain		0	0
Unrealized Loss		0	0
Estimated Fair Value		80	92
Classified as:
Total cash equivalents and marketable securities		80	92
Money market funds
Summary of cash equivalents and marketable securities:
Amortized Cost		47	43
Unrealized Gain		0	0
Unrealized Loss		0	0
Estimated Fair Value		47	43
Classified as:
Total cash equivalents and marketable securities		$ 47	$ 43