Earnings Per Share (Computation Of Basic And Diluted Earnings Per Share) (Detail) - 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 earnings per share:
Net income (loss)		$ (58)	$ 83	$ (497)	$ (145)
Less: undistributed earnings allocated to participating securities		0	5	0	0
Net income (loss) available to common shareholders		$ (58)	$ 78	$ (497)	$ (145)
Basic weighted average shares	[1]	52,588,533	78,686,542	62,391,826	82,813,523
Net income (loss) per basic common share		$ (1.11)	$ 1.00	$ (7.97)	$ (1.75)
Diluted earnings per share:
Net income (loss)		$ (58)	$ 83	$ (497)	$ (145)
Less: undistributed earnings allocated to participating securities		0	5	0	0
Net income (loss) available to common shareholders		$ (58)	$ 78	$ (497)	$ (145)
Diluted weighted average shares		52,588,533	78,686,542	62,391,826	82,813,523
Net income (loss) per diluted common share		$ (1.11)	$ 1.00	$ (7.97)	$ (1.75)
Potentially dilutive securities excluded from the calculation of diluted EPS because of antidilutive affect		4,800,000	4,500,000	4,800,000	4,500,000

[1] Includes 1.0 million and 1.1 million of participating securities that met the service condition and were eligible to receive nonforfeitable dividends or dividend equivalents for the three months ended September 30, 2020 and 2019, respectively. Includes 0.9 million and 1.0 million of participating securities that met the service condition and were eligible to receive nonforfeitable dividends or dividend equivalents for the nine months ended September 30, 2020 and 2019, respectively.