I was told, and the manual for the scanner I own confirms, that there is no law against listening to cordless phone conversations. It is strictly forbidden to listen to cellular phone conversations, and that is listed multiple times in the pages of the manual, but not once does it mention cordless phones.
A quick glance at the Scanner Laws webpage
... confirms this... It is illegal to listen to cell phone conversations, but cordless phone conversations are ok... as long as you don't record them without telling both parties.
That page should have all the information you need about scanner laws, both federal, and in each state.