S&P-style FFO / Net debt can be approximated from the provided annual report facts as:

- **FFO proxy**: cash flow from operations before working-capital movements and before cash taxes/CESE.
- Starting point: **Cash flows from / used in operations** = 4,200.324 million
- Working-capital related items included in operating cash flow:
  - Trade and other receivables: +405.817 million
  - Trade and other payables: +766.260 million
  - Personnel working capital: -142.137 million
  - Regulatory assets working capital: +502.859 million
- Net working-capital contribution = 405.817 + 766.260 - 142.137 + 502.859 = **1,532.799 million**
- Remove working-capital benefit: 4,200.324 - 1,532.799 = **2,667.525 million**
- Add back income tax and CESE cash outflow included in operating cash flow: +258.849 million
- Estimated **FFO** = 2,667.525 + 258.849 = **2,926.374 million EUR**

For **net debt**, use borrowings less cash and cash equivalents:

- Long-term borrowings = 15,782.604 million
- Current borrowings and current portion of non-current borrowings = 4,239.869 million
- Gross financial debt = 20,022.473 million
- Cash and cash equivalents = 4,900.205 million
- Estimated **net debt** = 20,022.473 - 4,900.205 = **15,122.268 million EUR**

Therefore:

- **FFO / Net debt** = 2,926.374 / 15,122.268 = **0.1935**, or about **19.4%**

<answer>19.4%</answer>