Investments (Securities Lending Programs) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Securities lending payable	$ 351	$ 604
Maturity Overnight [Member]
Investment [Line Items]
Securities lending payable	351
Maturity Overnight [Member] | Cash [Member]
Investment [Line Items]
Securities lending payable	291
Maturity Overnight [Member] | United States Government Securities [Member]
Investment [Line Items]
Securities lending payable	59
Maturity Overnight [Member] | Other Securities [Member]
Investment [Line Items]
Securities lending payable	$ 1