Financial Instruments - Unobservable Inputs, and Items Measured at Fair Value on a Recurring Basis that Used Significant Unobservable Inputs (Level 3) (Details) - Recurring [Member] - Level 3 [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jan. 29, 2016	Jan. 23, 2015	Jan. 29, 2016	Jan. 23, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 103	$ 108	$ 106	$ 106
Total unrealized gains (losses) included in other comprehensive income	0	0	(3)	2
Ending balance	103	108	103	108
Corporate debt securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1	9	1	9
Total unrealized gains (losses) included in other comprehensive income	0	0	0	0
Ending balance	1	9	1	9
Auction rate securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	102	99	105	97
Total unrealized gains (losses) included in other comprehensive income	0	0	(3)	2
Ending balance	$ 102	$ 99	$ 102	$ 99
Discounted cash flow [Member] | Auction rate securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Years to principal recovery			3 years
Illiquidity premium			6.00%
Minimum [Member] | Discounted cash flow [Member] | Auction rate securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Years to principal recovery			2 years
Maximum [Member] | Discounted cash flow [Member] | Auction rate securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Years to principal recovery			12 years