Future Policy Benefits - Liability for Future Policy Benefit Expected Future Policy Benefit Undiscounted (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Traditional Life
Liability for Future Policy Benefit, Expected Future Policy Benefit, Undiscounted [Abstract]
Expected future benefit payments	$ 2,996	$ 3,146
Expected future gross premiums	1,116	1,209
Liability For Future Policy Benefit, Expected Future Policy Benefit, Discounted [Abstract]
Expected future benefit payments	1,984	2,646
Expected future gross premiums	772	1,060
Immediate annuities
Liability for Future Policy Benefit, Expected Future Policy Benefit, Undiscounted [Abstract]
Expected future benefit payments	3,227	3,472
Expected future gross premiums	0	0
Liability For Future Policy Benefit, Expected Future Policy Benefit, Discounted [Abstract]
Expected future benefit payments	1,313	1,883
Expected future gross premiums	0	0
PRT
Liability for Future Policy Benefit, Expected Future Policy Benefit, Undiscounted [Abstract]
Expected future benefit payments	5,445	3,191
Expected future gross premiums	0	0
Liability For Future Policy Benefit, Expected Future Policy Benefit, Discounted [Abstract]
Expected future benefit payments	3,605	2,255
Expected future gross premiums	$ 0	$ 0