Reserve for Unpaid Losses and Loss Adjustment Expenses - GB Additional information (Details) - Group Benefits - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development [1]	$ (189)	$ (133)
Disability Insurance Policy [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development [1]	149	120
group life term, disability and accident [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development [1]	37	8
Supplemental Health
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development [1]	$ 3	$ 5