Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic (loss) earnings per share:
Income from operations attributable to common shareholders	$ (288)	$ 471	$ 213	$ 1,141
Net (loss) income available for common stock	$ (288)	$ 471	$ 213	$ 1,141
Weighted average common shares outstanding (in shares)	378,000,000	347,000,000	371,000,000	333,000,000
Basic earnings per share - continuing operations (in dollars per share)	$ (0.76)	$ 1.36	$ 0.57	$ 3.43
Diluted (loss) earnings per share:
Income from operations attributable to common shareholders	$ (288)	$ 471	$ 213	$ 1,141
Net (loss) income available for common stock	(288)	471	213	1,141
Net (loss) income available to common shareholders and assumed conversions	$ (288)	$ 471	$ 213	$ 1,141
Weighted average common shares outstanding (in shares)	378,000,000	347,000,000	371,000,000	333,000,000
Incremental shares from assumed conversions (in shares)	0	2,000,000	1,000,000	1,000,000
Adjusted weighted average shares - diluted (in shares)	378,000,000	349,000,000	372,000,000	334,000,000
Diluted earnings per share - continuing operations (in dollars per share)	$ (0.76)	$ 1.35	$ 0.57	$ 3.42
Stock option awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock-based compensation awards excluded from the computation of diluted earnings per share (in shares)	9,158,974	1,398,884	9,079,789	5,997,917