20 Average number of employees and personnel costs

    2017 2016 2015
Group (total)   216,454 220,582 226,332
Domestic   103,174 107,793 113,277
International   113,280 112,790 113,055
Non-civil servants   200,673 203,110 207,153
Civil servants (domestic, active service relationship)   15,781 17,472 19,179
Trainees and students on cooperative degree courses   6,559 7,510 7,942
Personnel costs millions of â‚¬ 15,504 16,463 15,856

The average headcount decreased by 1.9 percent compared with the prior year. This trend is largely attributable to a lower average domestic headcount, which was down by 4.3 percent. Staff restructuring measures in the Germany operating segment and the Group Headquarters & Group Services segment in particular contributed to this trend. In addition, Strato AG was deconsolidated from the Group Development operating segment as of March 31, 2017.

Outside of Germany, the average number of employees increased in total slightly by 0.4 percent due to staff increases both in the United States and the Europe operating segments as well as in the Group Headquarters & Group Services segment.

Personnel costs decreased by 5.8 percent year-on-year, due to the high restructuring expenses in connection with the early retirement ­arrangements for civil servants in the prior year and the lower average headcount in Germany. By contrast, higher average salaries of employees resulted in an increase in personnel costs.