Reserve for Unpaid Losses and Loss Adjustment Expenses - GB Additional information (Details) - Group Insurance Policies [Member] - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development	$ (284)	$ (162)
Long-term Disability [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development	195	105
group life term, disability and accident [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior incurral year development	$ 85	$ 55