Deferrals - postpone revenue and expense recognition even though cash has already been received or paid. Unearned revenue - the objective is to transfer the portion that has been earned to a revenue account, leaving the remainder as a liability. Revenue - the objective is to recognize all revenues that have been earned during the period, even if they have not been billed or collected. Expenses - the objective is to recognize all expenses incurred during the period, even though payment is not due until the next period. The contra asset is called accumulated depreciation.
All contra accounts have the opposite normal balances.
So, contra assets have a normal credit balance, contra liabilities have a normal dr.