What are the factors that may explain the similarity in credit quality but large differences in financial leverage between Consolidated Edison Inc., a regulated electric utility (Ticker: ED) that has an A- long-term credit rating from Standard & Poors, and a 50% net debt to capitalization ratio and Newmont Mining Corp., a global mining company (Ticker: NEM) that has a BBB+ long-term credit rating from Standard & Poors and a 9% net debt to capitalization ratio