Guarantees (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 26, 2015	Jul. 27, 2014	Jul. 26, 2015	Jul. 27, 2014
Estimated product warranty liabilities
SHIELD warranty charge	$ 15		$ 21
Balance at beginning of period	13	$ 8	8	$ 8
Additions	16	1	22	3
Deductions	(1)	(1)	(2)	(3)
Balance at end of period	$ 28	$ 8	$ 28	$ 8