Market Risk Benefits (MRB Valuation) (Details)		Sep. 30, 2025	Sep. 30, 2024
Minimum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate		0.50%	0.50%
Significant Unobservable Inputs Annuitization Rate		0.00%	0.00%
Maximum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate		27.30%	27.30%
Significant Unobservable Inputs Annuitization Rate		100.00%	100.00%
Weighted Average
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Lapse Rate	[1]	3.20%	3.40%
Significant Unobservable Inputs Annuitization Rate	[1]	4.90%	4.60%

[1] The weighted-average lapse and annuitization rates are determined by weighting each treaty's rates by the MRB contract's fair value.