Stockholders' Equity - Common Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		28 Months Ended
	Apr. 22, 2020	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Jul. 19, 2017
Class of Stock [Line Items]
Common share buy-back program, amount					$ 2,000
Common share buy-back program, average price per share				$ 17.71
Value of shares repurchased		$ 50	$ 2	$ 575
Per common share cash dividend declared for the period		$ 0.2625	$ 0.25
Per common share cash dividend paid in the period		$ 0.25	$ 0.20
Subsequent Event
Class of Stock [Line Items]
Per common share cash dividend declared for the period	$ 0.2625
Common stock
Class of Stock [Line Items]
Shares repurchased		3.6		32.0
Value of shares repurchased