At some point in their lives, nine out of 10 women will be solely responsible for their finances. This presents financial advisors with both an opportunity and a challenge, according to new insights Fidelity Investments reported Thursday from its 2012 Fidelity Millionaire Outlook Study.

The study identified key differences between male and female sole decision makers that make it imperative for financial advisors to involve both spouses in all planning.

Some $2 trillion are in motion each year because of divorce or death of a spouse, Meg Kelleher, executive vice president at Fidelity Institutional Wealth Services, said in a statement. “The reality is that your married clients could become single clients.

“Involving both spouses in planning gives both partners the skills to manage financially through a transition and can help protect your client relationships.”

The study found that one of the largest disconnects between genders was their approach to financial planning. Among those who work with financial advisors, women were nearly twice as likely as men to be interested in holistic financial guidance and planning to meet a specific lifestyle or goal.

Men, on the other hand, were focused on investment return, and were nearly twice as likely to say they were interested in achieving the greatest return on investment.

Of course, this does not mean that women are not interested in returns, only that they balance investment performance with broader considerations, Kelleher pointed out in a telephone interview with AdvisorOne.

The study also found that women were more conservative in their investment approach than men, with certificates of deposit/money market accounts/cash equivalents, individual domestic bonds and domestic bond mutual funds among their top five investments added in the last year.

Men favored riskier investment strategies such as individual domestic stocks; nearly twice as many men as women added these to their portfolio.

Women were 8% more likely than men to disagree with the statement: “I am willing to set aside a large portion of my portfolio for risky investments.”

And 61% of female respondents were more likely to agree that given the current market conditions, they are more comfortable putting their assets on the sidelines until things settle down.

The differences uncovered on how male and female millionaires use financial advice suggested that women may be a more attractive target than men for financial advisors, according to Fidelity.

Women were open to working with advisors, with 44% agreeing that they needed professional financial advice more now than in the past, and 49% without a current financial advisor saying they would like to find one they trust to manage their assets.

As well, the study found women more loyal to their advisors. Among respondents using a financial advisor, 45% of women and only 23% of men said they would be very likely to move their assets and relationship along with their primary advisor should that person switch firms.

Kelleher said that with so much money in play, advisors have a huge opportunity but risk losing out if they do not get to know their clients as individuals.  “One size does not fit all,” she said, as women may have different planning goals and be looking for different investment strategies.