Reserve for Unpaid Losses and Loss Adjustment Expenses - GB Additional information (Details) - Group Benefits - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development [1]	$ (403)	$ (323)
Disability Insurance Policy [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development [1]	369	275
group life term, disability and accident [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development [1]	25	40
Supplemental Health
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development [1]	$ 9	$ 10