The private equity firm has gained funding from several investors, including the asset management wing of General Electric and the Washington State Investment Board.
Warburg's initial target for the fund stood at $12 billion, the firm pointed out in an emailed statement.
Recent buys by the private equity company include a stake in bond insurer MBIA worth $1 billion.
Commenting on the announcement, Joseph Dear at Washington State said: "[Warburg] is well-positioned to perform, particularly in light of today's turbulent market conditions.''
The buyout market has been adversely affected by the credit crunch, figures cited by the news agency show.
So far in 2008, takeovers have been announced worth $89 billion - two-thirds down on the total by this time last year.