Willis Group Holdings P.L.C. CEO Dominic Casserley downplayed a fall in revenues at its North American unit as the London-based brokerage reported increased revenues overall on Tuesday.

Willis reported that commissions and fees grew 3.1% in the fourth quarter of 2014 to $939.0 million, while revenues totaled $958.0 million, an increase of 4.2% over the same period last year.

Organic commissions and fees, which exclude both the net impact of foreign currency movements and the net impact of acquisitions and disposals, grew 3.6% over the prior-year period, driven by strong growth in Willis International, Willis said Tuesday in a statement.

On a call with analysts Wednesday morning, Willis CEO Dominic Casserley said growth was led by the company's international segment, which grew 15.9% in the fourth quarter compared with last year and showed organic growth of 9.0% for 2014 on the back of new business.

The company's Willis North America Inc. segment, however, was down 2.1% for the quarter from the year-ago period and showed organic growth of 2.8% as the unit faced “headwinds” and a tough comparison with a very successful 2013 fourth quarter, Mr. Casserley said.

He added, however, that this quarter's weakness was “absolutely not” a harbinger of any future weakness going forward, pointing to North American net retention levels in the low 90% range.

Mr. Casserley also said the fourth-quarter weakness in the North American segment was “isolated” to the real estate and hospitality industry groups and the construction group, which was hampered by lower surety results.

The company's global group was largely flat, Mr. Casserley said, showing fourth-quarter growth of 0.3% and full-year organic growth of 1.4%.

Willis posted fourth-quarter net income of $76.0 million, an increase of 11.8% from the same period last year, while expenses for the quarter increased 5.8% to $819 million.

Fourth-quarter results benefitted from a $12 million gain reflecting a settlement related to a specialty book of business in the company's global segment, Willis said in its statement.

Full-year commissions and fees increased 6.7% to $3.77 billion, while revenues grew 4.0% to $3.80 billion.

For the full-year 2014, net income slipped 0.08% to $362 million, while expenses for the year increased 5.4% to $3.16 billion.

The company spent $36 million on its operational improvement program in 2014, less than the budgeted $40 million, according to Willis Chief Financial Officer John Greene, who also spoke on the call. He said savings from the program totaled $11 million, ahead of the budgeted $8 million.

Looking to 2015, Mr. Casserley said that while market conditions were “far from ideal,” he expected Willis would achieve mid-single-digit organic revenue growth.

In a note published Wednesday, Cliff Gallant, San Francisco-based analyst for Nomura Securities, said it was a good fourth quarter with strong overall revenues.

“For the second consecutive quarter, underlying revenue growth exceeded expense growth, and the operational improvement program is ahead of schedule,” Mr. Gallant said in his note, adding that “restructuring does not appear to be having a detrimental impact on revenues.”