Apple Inc. completed its second blockbuster bond sale in a year, tapping robust investor demand that has propelled corporate debt in 2014 to a larger gain than U.S. stocks.

Cupertino, Calif.-based Apple sold $12 billion of debt of varying maturities at interest rates that were mostly less than a percentage point above comparable U.S. Treasury debt, highlighting widespread faith in the iPhone maker's prospects. Investors flocked to the offering, placing more than $40 billion in orders.

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