Insurance Liabilities - Account balances by guaranteed minimum interest rates (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 100,523	$ 103,343
Account balance percentage	100.00%	100.00%
At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 57,036	$ 69,102
Account balance percentage	56.00%	67.00%
1 Basis Point - 50 Basis Points Above
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 7,773	$ 4,613
Account balance percentage	8.00%	4.00%
More than 50 Basis Points Above Minimum Guarantee
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 35,714	$ 29,628
Account balance percentage	36.00%	29.00%
Individual Retirement
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 55,920	$ 56,665
Individual Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	33,430	32,256
Individual Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 1% To 2%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	5,871	6,245
Individual Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	9,234	9,807
Individual Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	6,907	7,851
Individual Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	443	469
Individual Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	35	37
Individual Retirement | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Policyholder Account Balance	26,417	32,175
Individual Retirement | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	6,741	9,822
Individual Retirement | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 1% To 2%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	3,940	4,261
Individual Retirement | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	8,401	9,790
Individual Retirement | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	6,864	7,805
Individual Retirement | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	439	464
Individual Retirement | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	32	33
Individual Retirement | 1 Basis Point - 50 Basis Points Above
Policyholder Account Balance [Line Items]
Policyholder Account Balance	2,304	1,720
Individual Retirement | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	2,234	1,656
Individual Retirement | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 1% To 2%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	22	24
Individual Retirement | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	11	0
Individual Retirement | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	37	40
Individual Retirement | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Individual Retirement | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Individual Retirement | More than 50 Basis Points Above Minimum Guarantee
Policyholder Account Balance [Line Items]
Policyholder Account Balance	27,199	22,770
Individual Retirement | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	24,455	20,778
Individual Retirement | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 1% To 2%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	1,909	1,960
Individual Retirement | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	822	17
Individual Retirement | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	6	6
Individual Retirement | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	4	5
Individual Retirement | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	3	4
Group Retirement
Policyholder Account Balance [Line Items]
Policyholder Account Balance	37,372	39,242
Group Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	10,968	10,518
Group Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 1% To 2%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	5,888	6,484
Group Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	12,952	14,448
Group Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	641	690
Group Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	6,773	6,943
Group Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	150	159
Group Retirement | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Policyholder Account Balance	26,335	31,990
Group Retirement | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	2,197	3,726
Group Retirement | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 1% To 2%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	3,874	6,024
Group Retirement | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	12,700	14,448
Group Retirement | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	641	690
Group Retirement | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	6,773	6,943
Group Retirement | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	150	159
Group Retirement | 1 Basis Point - 50 Basis Points Above
Policyholder Account Balance [Line Items]
Policyholder Account Balance	3,973	2,051
Group Retirement | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	2,467	1,614
Group Retirement | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 1% To 2%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	1,347	437
Group Retirement | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	159	0
Group Retirement | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Group Retirement | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Group Retirement | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Group Retirement | More than 50 Basis Points Above Minimum Guarantee
Policyholder Account Balance [Line Items]
Policyholder Account Balance	7,064	5,201
Group Retirement | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	6,304	5,178
Group Retirement | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 1% To 2%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	667	23
Group Retirement | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	93	0
Group Retirement | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Group Retirement | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Group Retirement | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Life Insurance
Policyholder Account Balance [Line Items]
Policyholder Account Balance	7,231	7,436
Life Insurance | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Life Insurance | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 1% To 2%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	478	483
Life Insurance | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	1,953	1,982
Life Insurance | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	1,703	1,749
Life Insurance | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	2,879	2,998
Life Insurance | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	218	224
Life Insurance | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Policyholder Account Balance	4,284	4,937
Life Insurance | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Life Insurance | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 1% To 2%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	106
Life Insurance | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	9	235
Life Insurance | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	1,178	1,374
Life Insurance | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	2,879	2,998
Life Insurance | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	218	224
Life Insurance | 1 Basis Point - 50 Basis Points Above
Policyholder Account Balance [Line Items]
Policyholder Account Balance	1,496	842
Life Insurance | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Life Insurance | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 1% To 2%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	131	24
Life Insurance | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	866	635
Life Insurance | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	499	183
Life Insurance | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Life Insurance | 1 Basis Point - 50 Basis Points Above | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Life Insurance | More than 50 Basis Points Above Minimum Guarantee
Policyholder Account Balance [Line Items]
Policyholder Account Balance	1,451	1,657
Life Insurance | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Life Insurance | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 1% To 2%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	347	353
Life Insurance | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	1,078	1,112
Life Insurance | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	26	192
Life Insurance | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	0	0
Life Insurance | More than 50 Basis Points Above Minimum Guarantee | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 0	$ 0