Investments (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Fair value of collateral received at time of securities lending transactions	$ 564	$ 604
Securities Lending Transactions Ratio of Fair Value of Collateral Held To Securities On Loan	103.00%	102.00%
Securities lending transactions, initial collateral percentage value	102.00%