Nicole Kidman and Keith Urban are one of the sweetest celebrity couples in show business, and their marriage of nearly 14 years is a testament to how even stars can enjoy a successful relationship despite the pressures of their jobs.It seems that, for Kidman, it's actually Urban's ability to stay cool, calm and collected that has made their bond so strong.Thestar recently opened up in an interview with for the publication's upcoming May issue and revealed her sweet nickname for her handsome husband, which celebrates his chillness.According to Kidman, she lovingly refers to Urban as her «mellow muso» — muso being an Australian slang term for musician.«He’s pretty much the flip side of neurotic,» Kidman said, adding later that he would