Oddities with AT TIME ZONE and UTC offsets

I don't understand the difference between these two columns. America/Chicago timezone is UTC-6, so I expect both to return the same result: select timezone('America/Chicago', '2017-01-01 12:00:00'::TIMESTAMP AT TIME ZONE 'UTC'), timezone('UTC-6' , '2017-01-01 12:00:00'::TIMESTAMP AT TIME ZONE 'UTC'); However, the result is: 2017-01-01 06:00:00 | 2017-01-01 18:00:00 Also, this behavior is highly awkward, SELECT '1:00 -1'::time with time zone AT TIME ZONE '-1'; timezone ------------- 03:00:00+01 Can anyone explain this?