Guideline from STMicroelectronics on the basics of the two new USB Type-C™ and USB Power-Delivery standards. Link here (PDF)
This new reversible USB Type-C™ connector makes plug insertion more user friendly. The technology offers a single platform connector carrying all the necessary data. Using the power delivery protocol, it allows negotiation of up to 100 W power delivery to supply or charge equipment connected to a USB port, the objective being fewer cables and connectors, as well as universal chargers.
The USB Type-C™ connector provides native support of up to 15 W (5 V @ 3 A), extendable to 100 W (up to 20 V @ 5 A) with the optional USB Power Delivery feature.