The group said its board had been unanimous in rejecting last month's proposal from More Than owner RSA, which wanted to buy Aviva's home and motor insurance operations in the UK, Canada and Ireland.
Aviva said there were compelling strategic and financial benefits in continuing to run the general insurance business alongside its pensions and investments division.
It said this view was supported by a recent strategic review carried out in conjunction with external advisers.
Today's statement follows criticism from shareholders that Aviva rejected the RSA proposal without consulting them or notifying the market of the interest. Aviva shares rose by five per cent on Friday after RSA's move was revealed by the media.
While Aviva is the UK's leading general insurer with an estimated 15% market share, around 70 per cent of its world-wide profits come from life and pensions.
The two businesses operate in different cycles, with the steady cashflows of the general insurance arm seen as helping the whole business.
Aviva added that there were significant benefits from the composite model in terms of a single global brand, as well as cross-selling opportunities.
The company said that RSA's proposal would have left it with the pension liabilities of the general insurance business, as well as its operations in the Netherlands, France, Italy, Poland, Turkey and Singapore.
Aviva chairman Lord Sharman said: "Given the compelling strategic and financial benefits to Aviva shareholders of retaining the general insurance business, its upside potential and the terms offered by RSA, the board was unanimous in rejecting this proposal."
RSA tabled its proposal on July 28 and received a response from the Aviva board on August 6.
It is said to have lined up three heavyweight banks in Deutsche Bank, HSBC and BNP Paribas to work on a possible 5 billion rights issue to pay for any bid.
The cash call to investors would be one of the biggest in the insurance sector and exceed the company's market capitalisation of around 4.5bn.
RSA is likely to see significant synergies in linking the two general insurance businesses.