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Financial Instruments - Unobservable Inputs, and Items Measured at Fair Value on a Recurring Basis that Used Significant Unobservable Inputs (Level 3) (Details) - Recurring - Level 3 - USD ($)
$ in Millions
3 Months Ended
Jul. 28, 2017
Jul. 29, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance $ 45 $ 45
Total unrealized gains (losses) included in other comprehensive income 0 0
Ending balance 45 45
Corporate debt securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 1 1
Total unrealized gains (losses) included in other comprehensive income 0 0
Ending balance 1 1
Auction rate securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance 44 44
Total unrealized gains (losses) included in other comprehensive income 0 0
Ending balance $ 44 $ 44
Discounted cash flow | Auction rate securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Years to principal recovery 3 years  
Illiquidity premium 6.00%  
Minimum | Discounted cash flow | Auction rate securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Years to principal recovery 2 years  
Maximum | Discounted cash flow | Auction rate securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Years to principal recovery 12 years