Choosing two military ideas and one civic idea gives you a 2.5% reduction on war exhaustion per month.
Choosing two civic ideas and one military idea gives you a 1% increase on character loyalty per month.
Choosing one each of civic, military and economic ideas gives you a 5% increase on character wealth per month.
Choosing two civic ideas gives you a 1% increase on character popularity per month.
Choosing one each of economic and civic ideas gives you a 20% research points modifier.