Wal-Mart Stores said it will start disclosing directly to investors what it spends on lobbying on a state-by-state basis, responding to shareholder pressure to improve transparency on how the retailing giant seeks to influence public policy. The previously unreported move would make Wal-Mart the first constituent of the Dow Jones Industrial Average to break out state expenditures at that level of detail, drawing attention to spending that in some states reaches hundreds of thousands of dollars.