Other Insurance Liabilities and Separate Accounts - Undiscounted Expected Gross Premiums and Expected Future Benefit Payments (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Large Case Pensions
Liability for Future Policy Benefit, Activity [Line Items]
Expected future benefit payments	$ 3,337	$ 3,622
Expected gross premiums	0	0
Long-Term Care
Liability for Future Policy Benefit, Activity [Line Items]
Expected future benefit payments	3,237	3,269
Expected gross premiums	$ 419	$ 439