Market Risk Benefits - Schedule of market risk benefits (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Market Risk Benefit [Line Items]
Asset	$ 978	$ 743
Liability	4,519	4,635
Net	3,541	3,892
Individual Retirement
Market Risk Benefit [Line Items]
Asset	814	622
Liability	4,139	4,217
Net	3,325	3,595
Group Retirement
Market Risk Benefit [Line Items]
Asset	164	121
Liability	380	418
Net	$ 216	$ 297