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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 [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 |

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- Definition Number of years to principal recovery, used as an input to measure fair value. + References No definition available. + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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