Quiescent Current Analog Input ESP8266
That depends on if you're using a NodeMCU or a "naked" ESP8266.

The NodeMCU has a fixed voltage divider with 220K/100K resistors to ground, contributing about 10 &micro;A to quiescent current (plus the much smaller current caused by the ADC input impedance).

If you're using a NodeMCU you also have to worry about the USB-to-Serial chip and the on-board voltage stabilizer.

The input impedance of the ADC input of a "naked" ESP8266 is (probably) a lot higher, 1 or more MΩ, although it is almost impossible to find definitive numbers.