Stockholders' Equity (At-the-Market Offering Program) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, Shares Authorized		$ 26
Stock Issued During Period, Shares, New Issues		26.7
Stock Issued During Period, Value, New Issues	$ 190	$ 439	$ 190
Sale of Stock, Price Per Share		$ 16.46
Common Stock At The Market Sale Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period, Value, New Issues		$ 439