Exclusive: Pershing Square's Ackman eyes $1 billion-plus 'blank-check' company - sources

Billionaire investor William Ackman's hedge fund Pershing Square Capital Management has filed confidentially with U.S. regulators for an initial public offering (IPO) of a blank-check investment vehicle that could raise more than $1 billion and be the biggest of its kind, according to people familiar with the matter.