Insurance and Contractholder Liabilities - Other Segments - Liability Balance Details (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Other Segments [Member]
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Total liability for unpaid claims and claims expenses	$ 5,624	$ 5,467
Group Disability and Other [Member]
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Total liability for unpaid claims and claims expenses	4,866	4,684
Group Disability And Life [Member]
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Total liability for unpaid claims and claims expenses	4,674	4,491
Other Operations [Member]
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Total liability for unpaid claims and claims expenses	192	193
International Markets [Member]
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Total liability for unpaid claims and claims expenses	$ 758	$ 783