Just to elaborate, when power is sent over miles and miles of wire, it is sent as a very hight voltage. Now being a high voltage, the current can be smaller for the same power per the equation P(delivered)=E*I. Now, the line loss would be proportional to the current per P(loss)=I*R, where R is the resistance of the overhead wire. By sending power at very high voltage, the current (I in the equations) can be made very small, and thus the power loss in the last equation can be very small. Because the power is delivered as AC, the voltage can be stepped down just before it enters the building.