According to Pew research all three major news (US) outlets/networks plus CNN, BBC, Bloomberg, and others are left leaning.
There have been other studies that show this as well, one from UCLA in 2005 (so this has been going on a long time), Harvard, etc.
And yes, I know that some references are form right leaning outlets, but you would not really expect for those left leaning news outlets to come out and admit they are left leaning would you, esp. CNN "the most thrusted news".
Some news outlets on both sides are easily visible and expected, but the problem is that the so-called mainstream news organizations are left leaning. This is why Fox news started to give a different perspective than the left-liberal ideas that were permeating TV/cable. They have succeeded because they resonate with people who do not always agree with the liberal ideas.