Insurance companies may face higher tax liabilities in the future should former Vice President Joe Biden win the upcoming presidential election and get his proposed changes to the corporate tax structure passed through Congress, according to an S&P Global Market Intelligence analysis.

The Democratic presidential nominee's tax plan calls for raising the corporate tax rate to 28%, from the 21% rate established by the 2017 Republican tax overhaul, as well as doubling the tax rate to 21% from 10.5% on Global Intangible Low-Tax Income, or GILTI, earned by foreign subsidiaries of U.S. companies.

A third element of the plan is the imposition of a minimum tax rate of 15% on book income for corporations with more than $100 million in annual net income. The Tax Foundation said the minimum tax would be an alternative tax, with corporations paying either the minimum or their normal corporate income tax, whichever is greater.

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Taken at face value, the S&P Global analysis concludes that insurers would be looking at higher tax liabilities. The analysis, which was limited to U.S.-based insurance underwriters in select industries that trade on either the NYSE or Nasdaq, shows that on a pro rata basis, the minimum tax would have added a combined $703.5 million to the tax bills of four major life insurers if the plan was in effect in 2019.

Based on a strict 15% tax rate applied to 2019 net income, Voya Financial Inc. would have seen a $289 million increase, CNO Financial Group Inc. would have had a $176.3 million hike, MetLife Inc. would have had to pay an additional $133.3 million, and Lincoln National Corp. would have experienced a $104.9 million increase.

Phil Jacobs, a principal in the U.S. insurance tax sector for KPMG, said the impact of such a tax on insurers is unknown because Biden's plan does not specify how book income would be determined. He said companies will have difficulty determining which tax is higher for them until that is figured out.

"Insurance companies have really significant timing differences between book income and taxable income," Jacobs said in an interview. "So this is going to be another case where we're going to need to model to try to figure out which of those rates is going to be higher."

Overall, Biden's plan has many ideas, but not as many specifics. Ian Boccaccio, a global income tax leader for Ryan LLC, said the plan has not been fully fleshed out and is more of a "high-level directional signal" pointing where Biden wants to go, which is away from the corporate tax cuts that President Donald Trump championed.

"You can argue on either side that it was good or bad for the economy, but the bottom line is, this is going back toward a higher rate," Boccaccio said in an interview.

The lower rate may have been beneficial to other businesses, but Jacobs said that was not the case for insurers because they incurred "a number of specific rate increases ... that were part of that bill." He said there were revenue raisers, which he refers to as "pay-fors," in the Republican tax legislation that included changes to the ways acquisition costs are capitalized and how reserves are calculated.

Jacobs said those changes helped pay for the present 21% corporate income tax rate, but also had the general effect of increasing U.S. taxes for insurers. He said the industry could get "whiplash" if the rate goes from 21% to 28%, and should be modeling for the effects of the higher rate, but with the pay-fors included to see where they are relative to before the 2017 tax law — sometimes referred to as the Tax Cuts and Jobs Act, or TCJA — when the rate was 35%.

"If you go back to 2016 or 2017, before the TCJA, you had a 35% rate, but you didn't have these pay-fors," Jacobs said. "The interesting debate, which is company-specific, obviously, is when you wind up with a 28% rate, but these pay-fors from the TCJA are still in there, are companies better off? Are they worse off than they were before TCJA? I think that's an interesting question."