Basically there are fixed costs and variable costs. Usually the variable costs are the electricty cost per kwh, however the fixed costs are the delivery charges. These are usually fixed and even if you use 0 kwh in a single month you will still be charged them.
So if you want an accurate way, you can't divide your entire bill, you just need to find the formula they use for the fixed costs (it varies slightly by a 1-2 cent per kwh) and the variable costs which are easy to calculate.
Oh, wow! Good point. I've never had a bill that had fixed costs. In my area, all charges are variable based on usage.
Generation is billed at $0.0571 per kWh
Transmission is billed at $0.0133 per kWh
Distribution is billed at $0.0433 per kWh
Add in a few taxes and fees and you arrive at $0.125 overall.
I guess there is no universal simple method for everyone.