Insurance Liabilities - Account balances by guaranteed minimum interest rates (Details) - USD ($) $ in Millions	Mar. 31, 2023	Mar. 31, 2022
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 102,899	$ 102,927
Account balance percentage	100.00%	100.00%
At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 61,642	$ 71,268
Account balance percentage	60.00%	69.00%
1 Basis Point - 50 Basis Points Above
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 7,399	$ 4,787
Account balance percentage	7.00%	5.00%
More than 50 Basis Points Above Minimum Guarantee
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 33,858	$ 26,872
Account balance percentage	33.00%	26.00%
Individual Retirement
Policyholder Account Balance [Line Items]
Policyholder Account Balance	$ 57,225	$ 56,062
Individual Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	33,601	31,119
Individual Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 1% To 2%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	6,181	6,134
Individual Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	9,546	10,202
Individual Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	7,405	8,091
Individual Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	456	478
Individual Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	36	38
Individual Retirement | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Policyholder Account Balance	28,768	33,620
Individual Retirement | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	7,776	10,456
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	3,994	4,428
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	9,155	10,184
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	7,359	8,045
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	452	473
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	34
Individual Retirement | 1 Basis Point - 50 Basis Points Above
Policyholder Account Balance [Line Items]
Policyholder Account Balance	2,627	1,919
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	2,562	1,851
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	24	28
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	1	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	40	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	25,830	20,523
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	23,263	18,812
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	2,163	1,678
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	390	18
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	4	4
Group Retirement
Policyholder Account Balance [Line Items]
Policyholder Account Balance	38,324	39,323
Group Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	10,825	10,125
Group Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 1% To 2%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	6,266	6,734
Group Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	13,601	14,648
Group Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	658	702
Group Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	6,821	6,955
Group Retirement | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	153	159
Group Retirement | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Policyholder Account Balance	28,261	32,630
Group Retirement | At Guaranteed Minimum | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range Less Than 1%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	2,063	3,850
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	5,005	6,316
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	13,561	14,648
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	658	702
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	6,821	6,955
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	153	159
Group Retirement | 1 Basis Point - 50 Basis Points Above
Policyholder Account Balance [Line Items]
Policyholder Account Balance	3,661	2,095
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	2,713	1,684
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	908	411
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	40	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	6,402	4,598
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	6,049	4,591
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	353	7
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	0	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	7,350	7,542
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	480	483
Life Insurance | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 2% To 3%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	1,969	1,996
Life Insurance | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 3% To 4%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	1,733	1,781
Life Insurance | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 4% To 5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	2,946	3,054
Life Insurance | Policyholder Account Balance, Guaranteed Minimum Crediting Rate, Range From 5% To 5.5%
Policyholder Account Balance [Line Items]
Policyholder Account Balance	222	228
Life Insurance | At Guaranteed Minimum
Policyholder Account Balance [Line Items]
Policyholder Account Balance	4,613	5,018
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	104
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	28	246
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	1,417	1,388
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	2,946	3,052
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	222	228
Life Insurance | 1 Basis Point - 50 Basis Points Above
Policyholder Account Balance [Line Items]
Policyholder Account Balance	1,111	773
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	862	540
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	118	207
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	2
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	1,626	1,751
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	349	355
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	1,079	1,210
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	198	186
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