"Following a successful completion of the transaction, ING's stake in NN Group's outstanding capital is expected to decrease to approximately 42.4 percent from a current 54.8 percent," ING said in a statement.
"ING has previously announced that it intends to divest its remaining stake in NN Group over time," the Amsterdam- based bank added.
NN Group will buy back shares worth 150 million euros (USD 163 million) as part of the deal, ING said.
NN Group listed on the Amsterdam stock exchange last year in one of Europe's biggest initial public offerings for 2014.
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The sell-off is expected to be completed by the end of 2016.
Earlier restructuring led ING to sell its insurance businesses in Canada, Australia, New Zealand, Latin America and Asia as it sought to pay back the loan as well as an additional three billion euros in interest.
It paid the final amount in November last year, some six months ahead of schedule, and in February it announced its first dividend payment since being bailed out in 2008.
It posted pre-tax earnings of 905 million euros in 2013.