Commitments and Contingencies - Remaining Purchase Commitments and Estimated Capacity Fee Liability Requirements (Detail) € in Millions	Sep. 30, 2024 EUR (€)
Purchase Obligation Fiscal Year Maturity [Abstract]
Remaining Purchase Commitments, 2026	€ 4.2
Remaining Purchase Commitments, 2027	6.0
Remaining Purchase Commitments, 2028	6.0
Remaining Purchase Commitments, 2029	6.0
Remaining Purchase Commitments, 2030	6.0
Remaining Purchase Commitments, 2031	8.0
Remaining Purchase Commitments, 2032	8.0
Remaining Purchase Commitments, 2033	8.0
Remaining Purchase Commitments, 2034	4.4
Remaining Purchase Commitments, Total	56.6
Estimated Capacity Fees, 2025	1.5
Estimated Capacity Fees, 2026	2.0
Estimated Capacity Fees, 2027	1.0
Estimated Capacity Fees, 2028	1.0
Estimated Capacity Fees, 2029	1.0
Estimated Capacity Fees, 2030	1.0
Estimated Capacity Fees, 2031	0.5
Estimated Capacity Fees, 2032	0.5
Estimated Capacity Fees, 2033	0.5
Estimated Capacity Fees, 2034	0.5
Estimated Capacity Fees, Total	€ 9.5