Stockholders' Equity - Common Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		1 Months Ended	3 Months Ended		6 Months Ended		31 Months Ended
	Jul. 22, 2020	Mar. 31, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 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		$ 13.94					$ 17.71
Value of shares repurchased		$ 50			$ 50	$ 2	$ 575
Per common share cash dividend declared for the period			$ 0.2625	$ 0.25	$ 0.525	$ 0.50
Per common share cash dividend paid in the period			$ 0.2625	$ 0.25	$ 0.5125	$ 0.45
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			4.0		32.0