Because new versions of old questions get people riled, previous posts on the subject haven't been very complete, and for symbiosis across the various questions:
There are at least 3, possibly more, versions of West Side Story's "Somewhere" used in the TIAA-CREF commercials:
David Sylvian, of the band Japan
Ian McCulloch, of the band Echo and the Bunnymen
Chan Marshall, a.k.a. Cat Power
I may be wrong, but I believe:
The original-but-rare, deeper-voiced & gravelly version is David Sylvian.
The Ian McCulloch version is the most prevalent.
The only known version with a woman singing is Chan Marshall.
I have further found that none of these performers has rerecorded the song for release. They appear to be made-for-tv-commercial versions only (though I would truly love to be corrected on this statement).