Fair Value, Financial Assets and Liabilities Not Measured at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Carrying Amount [Member]
Assets [Abstract]
Other invested assets, primarily mortgage loans	$ 1,031	$ 1,068
Liabilities [Abstract]
Short term debt	186	35
Long term debt	8,919	10,042
Estimated Fair Value [Member]
Assets [Abstract]
Other invested assets, primarily mortgage loans	1,106	1,151
Liabilities [Abstract]
Short term debt	190	36
Long term debt	9,873	11,247
Estimated Fair Value [Member] | Level 2 [Member]
Liabilities [Abstract]
Short term debt		19
Long term debt	9,319	10,482
Estimated Fair Value [Member] | Level 3 [Member]
Assets [Abstract]
Other invested assets, primarily mortgage loans	1,106	1,151
Liabilities [Abstract]
Short term debt	190	17
Long term debt	$ 554	$ 765