CBA commissioned the report into CommInsure after a joint Fairfax Media and Four Corner's investigation exposed unethical practices such as the tampering of medical files and the denial of claims based on outdated definitions.

Deloitte's report said it did not identify "any systemic issues relating to historically declined claims" and "any evidence ... the claims handling processes are designed in a way that could systemically deliver poor customer outcomes".

Its recommendations included: staff training to keep them up to date on policy and procedural changes; better documentation to show how staff reached their conclusions; and better communication with claimants, especially in regards to claims denial.

Deloitte manually reviewed more than 200,000 email documents and interviewed 80 people, but "when assessing poor customer experience, [did] not interview the claimants", instead relying on existing paperwork.

Fairfax Media understands that investigations by law firm DLA Piper and accounting firm Ernst and Young, which interviewed claimants, will not be publicly released.

Deloitte also did not examine "remuneration or remuneration-related KPIs covering the claims", despite concerns about possible pay incentives tied to the denial of claims.

CBA said its claims staff received no financial incentives for declining or delaying claims.

It also said: "The Board is satisfied there is no evidence to support the allegation that medical opinions were maliciously deleted or tampered with."

More than 800 declined claims were independently reviewed by Deloitte. Its report states that nine customers, or 1 per cent, had benefits paid or increased, with 11 cases being reassessed.

One of the payments was worth $400,000.

The Australian Securities and Investments Commission is in the midst of investigating CommInsure, with its chief Greg Medcraft saying in October that CBA had "been found wanting".

ASIC's report isn't expected to be completed until later this year.

And in a submission to a parliamentary inquiry released last week, CommInsure whistleblower Benjamin Koh rejected the banks claims of an independent investigation after he raised allegations of a "simple alteration [that] could deny a claimant millions of dollars and save the company in the process".

Dr Koh, former chief medical officer, said he was told that anyone with basic IT skills was able to enter the system to alter the medical opinions of the company's doctors after a file he was examining went missing.

The Deloitte report concluded CommInsure isn't deliberately avoiding payouts or delaying payments to terminally ill customers, and there was nothing to suggest a culture where doctors are pressured or bullied by claims staff to change medical opinions.

"CommInsure doctors' medical opinions reflect the doctors," a CBA statement said. "The Board is reaffirmed in its confidence in the business and the values of our people, and is satisfied that there is not a culture of avoiding or wilfully denying claims."

In regards to out-of-date definitions, it conceded its definitions of a heart attack in May 2014 did not match that of the majority of its competitors, and in March 2016 it accelerated a planned update and backdated it.

"We then wrote to advise 600,000 current and former customers of this update," CBA said. "We actively searched for previously declined trauma claims and have paid $2.5 million to 17 eligible customers based on the changed definition."

CBA said Deloitte had access to more than 5 million emails and documents, manually reviewed 200,000 of them and conducted about 80 independent interviews. More than 150 people were involved.