Insurance and Contractholder Liabilities - Other Segments - Liability Balance Details (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Other Segments [Member]
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Total liability for unpaid claims and claims expenses	$ 5,857	$ 5,624	$ 5,494
Group Disability and Other [Member]
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Total liability for unpaid claims and claims expenses	5,076		4,763
Group Disability And Life [Member]
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Total liability for unpaid claims and claims expenses	4,887		4,584
Other Operations [Member]
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Total liability for unpaid claims and claims expenses	189		179
International Markets [Member]
Liability For Unpaid Claims And Claims Adjustment Expense [Line Items]
Total liability for unpaid claims and claims expenses	$ 781		$ 731