Stockholders' Equity - Common Equity (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended			25 Months Ended
	Jan. 22, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Jul. 19, 2017	Dec. 19, 2014
Class of Stock [Line Items]
Common share buy-back program, amount						$ 2,000
Value of shares repurchased		$ 2	$ 273	$ 250	$ 525
Common share buy-back program, average price per share					$ 18.18
Per common share cash dividend declared for the period		$ 1.00	$ 0.80	$ 0.50
Per common share cash dividend paid in the period		$ 0.95	$ 0.725	$ 0.50
Subsequent Event
Class of Stock [Line Items]
Per common share cash dividend declared for the period	$ 0.25
Equity distribution agreement | Class P
Class of Stock [Line Items]
Value of Stock Available for Sale Under Equity Distribution Agreement							$ 5,000
Share issued (in shares)		0	0	0
Common stock
Class of Stock [Line Items]
Shares repurchased		100,000	15,000,000	14,000,000	29,000,000