Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Basic earnings (loss) per share – continuing operations:
Income (loss) from continuing operations attributable to common shareholders	$ 739	$ 1,284	$ (457)
Participating securities dividends	0	0	0
Income (loss) from continuing operations available to common shareholders	$ 739	$ 1,284	$ (457)
Weighted-average shares of common stock outstanding (in shares)	373,000,000	340,000,000	326,000,000
Continuing operations (in dollars per share)	$ 1.98	$ 3.78	$ (1.40)
Diluted earnings (loss) per share – continuing operations:
Income (loss) from continuing operations attributable to common shareholders	$ 739	$ 1,284	$ (457)
Participating securities dividends	0	0	0
Income (loss) from continuing operations available to common shareholders	739	1,284	(457)
Income impact of assumed conversions	0	0	0
Income (loss) from continuing operations available to common shareholders and assumed conversions	$ 739	$ 1,284	$ (457)
Weighted average common shares outstanding (in shares)	373,000,000	340,000,000	326,000,000
Incremental shares from assumed conversions (in shares)	1,000,000	1,000,000	0
Adjusted weighted average shares – diluted (in shares)	374,000,000	341,000,000	326,000,000
Diluted (loss) earnings per share – continuing operations (in dollars per share)	$ 1.98	$ 3.77	$ (1.40)
Stock Compensation Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive stock option awards excluded from earnings per share, number of shares	9,066,753	4,511,802	8,852,706