Long-Duration Insurance Contracts - Weighted-Average Durations of LFPB (Details)	Sep. 30, 2024	Sep. 30, 2023
Whole Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average duration	17 years 8 months 12 days	17 years 9 months 18 days
Term Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average duration	16 years 4 months 24 days	16 years 4 months 24 days
Experience Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average duration	10 years 2 months 12 days	10 years 4 months 24 days
Limited Pay Whole Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average duration	21 years 6 months	22 years 2 months 12 days
Supplemental health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average duration	11 years 3 months 18 days	10 years 3 months 18 days
Life Contingent SPIA Retirement Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Weighted-average duration	8 years	7 years 7 months 6 days