I thought one version was by Low, but I guess that is Cat Power eh? I always get her voice confused with the girl from Low...

According to the official answer I got from TIAA CREF when I asked this question:

There are two artists singing the vocals to 'Somewhere' in our
television commercials. Below is a brief bio of each artist:

David Sylvian sings the 60-second version. Born David Batt in Kent,
England on February 23, 1958. Sylvian founded a group called 'Japan' in
1974 and served as their primary singer/songwriter throughout the
group's eight-year existence. Writer, producer, singer, musician,
co-conspirator of the 'new romantic' movement of the late '70s, photographer,
painter and installation artist, Sylvian is essentially an artist's
artist. Following the 1982 dissolution of Japan, the group's onetime front
man, David Sylvian, staked out a far-ranging and esoteric career of
solo projects.

Ian McCulloch sings the 30-second version. The front man of
Liverpool's Echo & the Bunnymen, Ian McCulloch got his start with Pete Wylie and
Julian Cope as the Crucial Three. This band lasted just over a month
and McCulloch formed Echo & the Bunnymen with Will Sergeant in 1978.
Echo went on to become one of England's most successful and important pop
bands throughout the 80's. McCulloch left the band in late 1988 to
pursue a solo career.