Long-Duration Insurance Contracts - Actual and Expected Experience of Mortality Rate and Lapse Rate (Details)	Sep. 30, 2025	Sep. 30, 2024
Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Mortality / Morbidity, Actual experience	0.80%	0.70%
Mortality / Morbidity, Expected experience	0.80%	0.80%
Lapses, Actual experience	3.50%	3.00%
Lapses, Expected experience	3.80%	4.40%
Term Life | Minimum
Liability for Future Policy Benefit, by Product Segment [Line Items]
Mortality / Morbidity, Actual experience	0.10%	0.10%
Mortality / Morbidity, Expected experience	0.10%	0.10%
Lapses, Actual experience	3.80%	3.70%
Lapses, Expected experience	5.10%	5.40%
Term Life | Maximum
Liability for Future Policy Benefit, by Product Segment [Line Items]
Mortality / Morbidity, Actual experience	0.70%	0.30%
Mortality / Morbidity, Expected experience	1.30%	0.80%
Lapses, Actual experience	13.60%	28.60%
Lapses, Expected experience	13.40%	12.80%
Experience life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Mortality / Morbidity, Actual experience	1.80%	1.90%
Mortality / Morbidity, Expected experience	1.90%	1.70%
Lapses, Actual experience	3.80%	2.90%
Lapses, Expected experience	3.00%	3.00%
Limited-Pay Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Mortality / Morbidity, Actual experience	0.50%	0.20%
Mortality / Morbidity, Expected experience	0.30%	0.30%
Lapses, Actual experience	3.30%	3.90%
Lapses, Expected experience	4.00%	4.70%
Supplemental health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Mortality / Morbidity, Actual experience	27.10%	28.90%
Mortality / Morbidity, Expected experience	26.50%	26.30%
Lapses, Actual experience	10.70%	9.40%
Lapses, Expected experience	10.20%	9.70%