That fee was "a key element" to a projected 200 basis point improvement in IAG's reported insurance margin, Hawkins said. "It is 3 per cent of our equity plus a fairly sizeable fee exchange commission."
The company didn't release details of the fee, preferring to give guidance instead, which for 2015 is for gross written premium growth (GWP) at the lower end of the 17 per cent to 20 per cent it gave in February and for reported insurance margin of 10.5 per cent to 12.5 per cent.
For 2016, GWP growth is forecast at zero to 3 per cent, with an insurance margin of 14 per cent to 16 per cent.
Under the agreement, IAG has an option to place up to a further 5 per cent of its shares to Berkshire within 24 months and the US firm can move up to a maximum 14.9 per cent stake. It must maintain its initial stake for the term of the quota agreement.
Wilkins said the deal reduces IAG's capital requirements by about A$700 million through 2020, including about A$400 million in 2016, and reduces IAG's catastrophe requirement.
"This reduces volatility in future earnings and gives us significant scope to pursue growth and consider capital management," Wilkins said.
IAG businesses underwrite more than A$11 billion of premiums a year through brands including NRMA Insurance, CGU and Swann in Australia, NZI State, AMI and Lumley Insurance in New Zealand, and various brands in its target Asian markets of India, Malaysia, China, Vietnam and Indonesia.
IAG said Berkshire's investment would have "a modest dilutionary effect in the short-term" but would provide capital and operational benefits longer term.