Inverting Op Amp Output Voltage
Inside each op-amp are two little transistor men as illustrated in Win Hill's Art of Electronics: 



In this case say C is connected to V+ and E is connected to the output. There's another one (not shown) standing on his head say with C connected to V- and E connected to the output. 

All that transistor man can do is adjust that variable resistor according to Ib (which comes from the input stages of the amplifier). The best he can do is turn the pot all the way down so that the output is connected to the supply (and in fact he can't quite get there). 

So all the op-amp can do is pull its output somewhere between the two supply lines, there is no internal voltage source to allow it to exceed the supplies. Most op-amps if not too heavily loaded can pull the output to within a volt or two of the supply rails, some much closer, especially if lightly loaded.