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