No, you don't get it at all. The outstanding shares will be converted to new shares at a ratio that roughly keeps existing shareholders whole. What matters is how many total shares @ $20 each will be sold. Let's say they sell 185mm shares, raising $3.7bn. This is amount of money that the bank receives for the 57.7% of the company that it is selling to the public, and it implies a total market cap of $6.4bn. Since there are 142mm shares currently outstanding, this would correspond to a current share price of $45. Existing shareholders would receive approximately 225 new shares for each 100 shares currently owned.
I'm still trying to figure out if this is a buy or not.