Earnings Per Share (Schedule of Basic and Diluted EPS ) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net (loss) income	$ (368)	$ 753	$ (429)	$ 1,479
Preferred stock dividends	0	0	(16)	(16)
Net (loss) income available to common stockholders	(368)	753	(445)	1,463
Income allocated to participating securities	(1)	(6)	(1)	(11)
Net (loss) income allocated to common stockholders	(369)	747	$ (446)	$ 1,452
Income allocated to participating securities, diluted	(1)	(6)
Net income (loss) allocated to common stockholders, diluted	$ (369)	$ 747
Denominator:
Weighted-average shares of common stock outstanding	306	322	307	325
Weighted Average Number Diluted Shares Outstanding Adjustment	0	1	0	1
Weighted-average shares of common stock outstanding and common stock equivalents	306	323	307	326
Basic (loss) earnings per common share (in dollars per share)	$ (1.20)	$ 2.32	$ (1.45)	$ 4.46
Diluted (loss) earnings per common share (in dollars per share)	$ (1.20)	$ 2.32	$ (1.45)	$ 4.46