Someone

SELECT DISTINCT
  EXTRACT(month from "contas_pagar"."vencimento") as "mes",
  EXTRACT(year from "contas_pagar"."vencimento") as "ano",
  (SELECT
     coalesce(sum("contas_pagar_liq"."valor_pagamento"),0)
    FROM
      "contas_pagar_liq"
    WHERE
      "contas_pagar_liq"."vencimento" < CURRENT_DATE
      AND EXTRACT(month from "contas_pagar_liq"."vencimento") = EXTRACT(month from "contas_pagar"."vencimento")
      AND EXTRACT(year from "contas_pagar_liq"."vencimento") = EXTRACT(year from "contas_pagar"."vencimento"))+(SELECT coalesce(sum("contas_pagar_liq"."valor"-"contas_pagar_liq"."valor_pagamento"),0)
    FROM
      "contas_pagar_liq"
    WHERE
      "contas_pagar_liq"."vencimento" < CURRENT_DATE
      AND EXTRACT(month from detalhe.vencimento) = EXTRACT(month from principal.vencimento)
      AND EXTRACT(year from detalhe.vencimento) = EXTRACT(year from principal.vencimento)) as "carteira",
  (SELECT
    coalesce(sum("contas_pagar_liq"."valor_pagamento"),0)
   FROM
     "contas_pagar_liq"
   WHERE
     "contas_pagar_liq"."dataliq" < CURRENT_DATE
     AND EXTRACT(month from "contas_pagar_liq"."dataliq") = EXTRACT(month from "contas_pagar"."vencimento")
     AND EXTRACT(year from "contas_pagar_liq"."dataliq") = EXTRACT(year from "contas_pagar"."vencimento")) as "realizado",
  coalesce(sum("contas_pagar"."valor"-"contas_pagar"."valor_pagamento"),0) as "aPagar"
FROM
  "contas_pagar"
WHERE
  "contas_pagar"."vencimento" < CURRENT_DATE
GROUP BY
  2,1
ORDER BY
  2,1