Reserve for Unpaid Losses and Loss Adjustment Expenses - GB Additional information (Details) - Group Insurance Policies [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development	$ (120)	$ (127)
Long-term Disability [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development	105	85
group life term, disability and accident [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development	$ 10	$ 40