Just sharing directly from blog.coinbase.com -
"Announcing instant bitcoin, ethereum and litecoin purchases on Coinbase
We are excited to announce the ability for customers to instantly purchase digital currency using a US bank account. Previously, customers who purchased using a bank account had to wait several days before receiving their digital currency. Customers can now buy up to $25,000* and receive access to their digital currency immediately.
Our mission is to make Coinbase the most trusted, safe, and easy-to-use digital currency exchange. Instant purchases make it significantly easier and faster for customers to invest in the digital currency ecosystem. Reducing the time to receive digital currency has been a highly requested feature and we are pleased to provide this improved experience for our customers.
Instant bank purchases are now live for many of our customers in the US, and we will expand availability over the coming months. You will receive an email when instant purchases become available for your account.If you don’t have a Coinbase account, sign up for one here.
*Note: maximum instant purchase limit is $25,000. Individual limits may vary. "
Source: https://blog.coinbase.com/announcing-instant-bitcoin-ethereum-and-litecoin-purchases-on-coinbase-c29d8a94e152