Insurance and Contractholder Liabilities - Other Segments - Reconciliation to the Liability for Unpaid Claims and Claims Expense (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Other Segments [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liability for unpaid claims and claims expenses	$ 5,624	$ 5,467
International Markets [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liability for unpaid claims and claims expenses	758	783
Group Disability And Life [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for unpaid claims and claims expenses, net of reinsurance	4,569
Reinsurance recoverable on unpaid claims	105
Total liability for unpaid claims and claims expenses	4,674	4,491
Other Operations [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liability for unpaid claims and claims expenses	192	$ 193
Long-term Disability [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for unpaid claims and claims expenses, net of reinsurance	3,975
Long-term Disability [Member] | Group Disability And Life [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for unpaid claims and claims expenses, net of reinsurance	3,975
Reinsurance recoverable on unpaid claims	94
Other Short-duration Insurance Product Line [Member] | Group Disability And Life [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for unpaid claims and claims expenses, net of reinsurance	594
Reinsurance recoverable on unpaid claims	$ 11