Fair Value, Financial Assets and Liabilities Not Measured at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Carrying Amount [Member]
Assets [Abstract]
Other invested assets, primarily mortgage loans	$ 1,068	$ 994
Liabilities [Abstract]
Short term debt	35	75
Long term debt	10,042	11,443
Estimated Fair Value [Member]
Assets [Abstract]
Other invested assets, primarily mortgage loans	1,151	1,025
Liabilities [Abstract]
Short term debt	36	75
Long term debt	11,247	11,510
Estimated Fair Value [Member] | Level 2 [Member]
Liabilities [Abstract]
Short term debt	19	9
Long term debt	10,482	10,884
Estimated Fair Value [Member] | Level 3 [Member]
Assets [Abstract]
Other invested assets, primarily mortgage loans	1,151	1,025
Liabilities [Abstract]
Short term debt	17	66
Long term debt	$ 765	$ 626