One thousand million (1,000,000,000 or 109).
EUR 456 billion = EUR 456,000,000,000.
Often abbreviated to 'bn' or 'Bn'. For example EUR 456bn.
Historically - in the UK and some other countries - 'billion' used to refer mathematically to 1,000,000,000,000 (or 1012).
This historical usage never became well-established in finance, and is now - for most practical purposes - defunct.