Fair Value , Carrying Amount, Estimated Fair Value and Level of Fair Value Hierarchy of Company's Financial Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Estimate Fair Value [Member]
Assets [Abstract]
Other invested assets, primarily mortgage loans	$ 1,036	$ 1,025
Liabilities [Abstract]
Short term debt	882	75
Long term debt	9,141	11,510
Carrying Amount [Member]
Assets [Abstract]
Other invested assets, primarily mortgage loans	1,021	994
Liabilities [Abstract]
Short term debt	2,459	75
Long term debt	9,496	11,443
Level 2 [Member] | Estimate Fair Value [Member]
Liabilities [Abstract]
Short term debt	844	9
Long term debt	8,444	10,884
Level 3 [Member] | Estimate Fair Value [Member]
Assets [Abstract]
Other invested assets, primarily mortgage loans	1,036	1,025
Liabilities [Abstract]
Short term debt	38	66
Long term debt	$ 697	$ 626