Citizens Financial Group Inc, the US unit of the Royal Bank of Scotland, filed with US regulators for an initial public offering of common stock that would raise about $100 million. Morgan Stanley, Goldman, Sachs & Co and J.P. Morgan are the lead underwriters for the IPO, the company said in a filing with the US Securities and Exchange Commission on Monday. The amount of money a company says it plans to raise in its first IPO filings is used to calculate registration fees. The final size of the IPO could be different.