Foreign investors, including promoter Vodafone group, are likely to invest around Rs 18,000 crore in the rights issue of Vodafone Idea. The company's Rs 25,000 crore rights issue will open on April 10. Any foreign funding above Rs 5,000 crore requires Cabinet approval. The Cabinet had on February 28 cleared the company's FDI proposal. While Vodafone Group's entire funding will be considered as foreign investment in the rights issue, Aditya Birla Group may also route funds from its foreign entities.