Long-Duration Insurance Contracts - Weighted-Average Durations of LFPB (Details)	Sep. 30, 2025	Sep. 30, 2024
Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average duration	20 years 3 months 18 days	17 years 8 months 12 days
Term Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average duration	16 years 2 months 12 days	16 years 4 months 24 days
Experience life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average duration	9 years 7 months 6 days	10 years 2 months 12 days
Limited-Pay Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average duration	25 years 6 months	21 years 6 months
Supplemental health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average duration	11 years 8 months 12 days	11 years 3 months 18 days
SPIA (life contingent)
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average duration	7 years 4 months 24 days	8 years