{% set totalOrders = 0 %}
{% for order in craft.commerce.orders.customer(craft.commerce.customer).find() %}
  {% set totalOrders = totalOrders + order.totalPrice|currency(order.currency) %}
{% endfor %}
{{ totalOrders|currency(order.currency) }}

{% set cart = craft.commerce.cart %}
{% set totalOrders = 0 %}

{% for order in craft.commerce.orders.customer( craft.commerce.customer ).find() %}
  {% set totalOrders = totalOrders + order.totalPrice %}
{% endfor %}

{{ totalOrders|currency( cart.currency ) }}