本論文採用或有請求權分析架構，探討透過總報酬交換交易，在資本管制下，商業銀行採行同一屋簷營運模式之擴張證券與保險服務業務，如何決定銀行的最適利差，特別是在通過GLBA後之金融環境情況下。我們發現到，銀行利差和非利息收入與銀行的證券避險需求和保險業務呈現正向相關，但與銀行的資金需求呈現負向相關；同時也發現到，銀行非利息收入在利差變動的情況下有類似的論證。顯示商業銀行兼營投資銀行業務將使得綜合績效上升。此外，如果政府降低資本適足的額度，商業銀行將會有較強烈的動機去擴張投資銀行的業務。 The Gramm-Leach-Bliley Act (GLBA) of 1999 allows commercial bank expansion into investment banking of securities and insurance activities without limit in subsidiaries separate from commercial banks. This paper demonstrates how securities hedging, insurance underwriting, and capital regulation through the total return swap approach jointly determine the optimal bank interest margin under the same roof. We find that the bank’s interest margin and noninterest income are positively related to the bank’s securities hedging demand, and to the insurance underwriting provision, but negatively related to the bank capital requirement. We also find that the results of the bank’s noninterest income follow a similar argument as in the case of a change in interest margin. The results show that the combined production of commercial banking expansion into investment banking enhances the bank’s synergistic gains. In addition, if regulators reduce capital charges, a commercial bank will have a strong incentive to expand its investment banking activities. This suggests obvious diversification benefits from the return to investment banking under the same roof.