|Millions of euro|
|at Dec. 31, 2020||at Dec. 31, 2019||Change|
|Amounts due from institutional market operators||1,265||732||533||72.8%|
|Advances to suppliers||309||314||(5)||-1.6%|
|Amounts due from employees||30||28||2||7.1%|
|Amounts due from others||956||1,084||(128)||-11.8%|
|Sundry tax assets||848||797||51||6.4%|
|Accrued operating income and prepayments||170||160||10||6.3%|
Amounts due from institutional market operators include amounts due in respect of the Italian system in the amount of €890 million (€450 million at December 31, 2019) and the Spanish system in the amount of €337 million (€254 million at December 31, 2019). The increase is essentially attributable to the increase in amounts due in Italy in respect of the Energy and Environmental Services Fund, mainly held by e-distribuzione (€207 million) and Servizio Elettrico Nazionale (€249 million), primarily connected with equalization mechanisms.
The increase of €51 million in sundry tax assets is mainly attributable to an increase in credits for indirect taxes and duties.
Amounts due from others decreased mainly due to a decline in advances paid to third parties, a reduction in receivables in respect of pension and insurance institutions and a decrease in other sundry amounts.