Investments (Available-for-sale Investments) (Details Textual) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Cash and cash equivalents	$ 687		$ 677
Total realized gains	37	$ 2
Total realized losses	$ 4	$ 8