Abstract. In 1973/74 Bennett and (independently) Carl proved that for 1 ≤ u ≤ 2 the identity map id: u → 2 is absolutely (u, 1)-summing, i. e., for every unconditionally summable sequence (xn) in u the scalar sequence ( xn 2 ) is contained in u, which improved upon well-known results of Littlewood and Orlicz. The following substantial extension is our main result: For a 2-concave symmetric Banach sequence space E the identity map id : E → 2 is absolutely (E, 1)-summing, i. e., for every unconditionally summable sequence (xn) in E the scalar sequence ( xn 2 ) is contained in E. Various applications are given, e. g., to the theory of eigenvalue distribution of compact operators, where we show that the sequence of eigenvalues of an operator T on 2 with values in a 2-concave symmetric Banach sequence space E is a multiplier from 2 into E. Furthermore, we prove an asymptotic formula for the k-th approximation number of the identity map id : n 2 → En, where En denotes the linear span of the first n standard unit vectors in E, and apply it to Lorentz and Orlicz sequence spaces.