Marketable Securities (Tables)

6 Months Ended

Jul. 31, 2016

Schedule of Available-for-sale Securities [Line Items]

Cash Equivalents and Marketable Securities

	July 31, 2016
	Amortized Cost		Unrealized Gain		Unrealized Loss			Estimated Fair Value
	(In millions)
Corporate debt securities	$	1,972	$	5	$	(1	)	$	1,976
Debt securities of United States government agencies	1,046		2		—			1,048
Debt securities issued by United States Treasury	809		3		—			812
Asset-backed securities	369		1		—			370
Mortgage-backed securities issued by United States government-sponsored enterprises	175		3		(1		)	177
Foreign government bonds	80		—		—			80
Money market funds	47		—		—			47
Total	$	4,498	$	14	$	(2	)	$	4,510
Classified as:
Cash equivalents								$	57
Marketable securities								4,453
Total								$	4,510

	January 31, 2016
	Amortized Cost		Unrealized Gain		Unrealized Loss			Estimated Fair Value
	(In millions)
Corporate debt securities	$	1,903	$	1	$	(3	)	$	1,901
Debt securities of United States government agencies	1,170		1		(1		)	1,170
Debt securities issued by United States Treasury	800		1		—			801
Asset-backed securities	435		—		—			435
Mortgage-backed securities issued by United States government-sponsored enterprises	229		3		(1		)	231
Foreign government bonds	92		—		—			92
Money market funds	43		—		—			43
Total	$	4,672	$	6	$	(5	)	$	4,673
Classified as:
Cash equivalents								$	232
Marketable securities								4,441
Total								$	4,673

Schedule of Unrealized Loss on Investments [Table Text Block]

	Less than 12 months				12 months or greater				Total
	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
	(In millions)
Corporate debt securities	$	263	$	1	$	98	$	—	$	361	$	1
Mortgage-backed securities issued by United States government-sponsored enterprises	54		1		31		—		85		1
	$	317	$	2	$	129	$	—	$	446	$	2

Schedule of Amortization Cost and Estimated FV of CE and MS

	July 31, 2016				January 31, 2016
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
	(In millions)
Less than 1 year	$	1,846	$	1,847	$	1,619	$	1,619
Due in 1 - 5 years	2,591		2,601		3,019		3,020
Mortgage-backed securities issued by United States government-sponsored enterprises not due at a single maturity date	61		62		34		34
Total	$	4,498	$	4,510	$	4,672	$	4,673