Reserve for Future Policy Benefits and Contractholder Funds - Schedule of undiscounted and discounted expected gross premiums and expected future benefits and expenses (Details) - USD ($) $ in Millions	Mar. 31, 2023	Mar. 31, 2022
Accident and health insurance
Liability for Future Policy Benefit, Activity [Line Items]
Expected future gross premiums, undiscounted	$ 5,068	$ 5,219
Expected future gross premiums, discounted	3,671	4,137
Expected future benefits and expenses, undiscounted	3,351	3,453
Expected future benefits and expenses, discounted	2,335	2,629
Traditional life
Liability for Future Policy Benefit, Activity [Line Items]
Expected future gross premiums, undiscounted	721	652
Expected future gross premiums, discounted	500	500
Expected future benefits and expenses, undiscounted	1,008	972
Expected future benefits and expenses, discounted	$ 547	$ 625