Reserve for Unpaid Losses and Loss Adjustment Expenses - GB Additional information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Long-term Disability [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development [2]	$ 230	$ 175
group life term, disability and accident [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development [2]	65	$ 25
Accident and Health Insurance Product Line [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development [2]	$ 20