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Reserve for Unpaid Losses and Loss Adjustment Expenses - Additional Information (Details) - Group Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior accident year development [1]	$ (445)	$ (410)	$ (324)
Group long-term disability
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior accident year development [1]	365	340	230
Group life and accident, excluding premium waiver
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior accident year development [1]	65	$ 60	$ 90
Group supplemental health
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior accident year development [1]	$ 15