Congress, congressional

Always capitalize Congress in U.S. context:

            the Congress, Ninth Congress, 10th Congress, 63rd Congress

            Congresswoman Christine Ullrich, the U.S. congresswoman

            member of Congress, congressman (although congressman/

                        congresswoman technically refer to any member of

                        Congress, the terms are often used as titles for representative)

joint meeting, joint session

Always capitalize in Civil War context:

            Confederate Congress, the Congress

Also capitalize with name of foreign country if congress is part of proper name:

            Argentine Congress, the congress

but     Guatemalan congress (Legislative Assembly)

Speaker of the House Paul Ryan; House Speaker Paul Ryan; the speaker of the House; the speaker