The Tax Cuts and Jobs Act changed the dividends received deduction for corporations.
Through December 31, 2017
Dividends received by a corporation from another corporation were 70% excluded from income for less than 20% owned domestic corporations and 80% excluded from income for more than 20% owned domestic corporations.
Effective for tax years beginning after December 31, 2017
The percentage excluded from income is decreased from 70% to 50%, and from 80% to 65%.
The general impact of this will be to keep the tax on dividends received by a corporation substantially the same under current and prior law. The combination of lower exclusions and lower tax rates creates almost the same actual tax due on dividends received.