Reserve for Unpaid Losses and Loss Adjustment Expenses - GB Additional information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Long-term Disability [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development [2]	$ 293	$ 265
group life term, disability and accident [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development [2]	50	$ 45
Accident and Health Insurance Product Line [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development [2]	$ 19