Looking at the Catholic Study Bible I see
He said to them, "This is my blood of the covenant, which will be shed for many.http://www.usccb.org/nab/bible/mark/mark14.htm#foot8
8  Which will be shed: see the note on Matthew 26:27-28. For many: the Greek preposition hyper is a different one from that at Matthew 26:28 but the same as that found at Luke 22:19, 20 and 1 Cor 11:24. The sense of both words is vicarious, and it is difficult in Hellenistic Greek to distinguish between them. For many in the sense of "all," see the note on Matthew 20:28.
And Matthew 20:28 goes
Just so, the Son of Man did not come to be served but to serve and to give his life as a ransom for many."http://www.usccb.org/nab/bible/matthew/matthew20.htm#foot11
11  Ransom: this noun, which occurs in the New Testament only here and in the Marcan parallel (Matthew 10:45), does not necessarily express the idea of liberation by payment of some price. The cognate verb is used frequently in the LXX of God's liberating Israel from Egypt or from Babylonia after the Exile; see Exodus 6:6; 15:13; Psalm 77:16 (76 LXX); Isaiah 43:1; 44:22. The liberation brought by Jesus' death will be for many; cf Isaiah 53:12. Many does not mean that some are excluded, but is a Semitism designating the collectivity who benefit from the service of the one, and is equivalent to "all." While there are few verbal contacts between this saying and the fourth Servant Song (Isaiah 52:13-53:12), the ideas of that passage are reflected here.