Do the logic gate inputs of 74HCXX integrated circuits exhibit a high impedance?
With the 74HC series and other logic families that include a large number of devices rather than the individual datasheets repeating the basic characteristics of the logic family normally the manufacturers publish some form of family guide. For example from NXP Semiconductor:

74HC/T HCMOS Family Specifications

Page 28 shows some more detailed information on the inputs of the 74HC series and mentions a current flow of only a few nA. There's also the host of other information you might be used to seeing in a complete datasheet.