An insurance money makes its money from the premiums people pay and spends money on claims. Once a claim is made, there is a period of time before the company must pay it.

Even at break-even, an insurance company must keep a large amount of cash on hand to pay future claims. This is called float. Even though the company does not 'own' the money, it is free to invest it while it holds it. Buffet has used Geico and other insurers primarily as vehicles to invest their float.