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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic earnings per share: [Abstract]
Net income (loss)	$ (45)	$ (267)	$ (289)	$ (1,568)
Net income (loss) available to common stockholders	$ (45)	$ (267)	$ (289)	$ (1,568)
Basic weighted average shares	89,490,267	122,967,924	89,075,892	126,643,642
Basic	$ (0.5)	$ (2.17)	$ (3.24)	$ (12.38)
Diluted earnings per share: [Abstract]
Net income (loss)	$ (45)	$ (267)	$ (289)	$ (1,568)
Net income (loss) available to common stockholders	$ (45)	$ (267)	$ (289)	$ (1,568)
Basic weighted average shares	89,490,267	122,967,924	89,075,892	126,643,642
Diluted weighted average shares	89,490,267	122,967,924	89,075,892	126,643,642
Diluted	$ (0.5)	$ (2.17)	$ (3.24)	$ (12.38)
Unvested Restricted Stock And Units That Receive Nonforfeitable Dividends Or Dividend Equivalents That Have Met Service Condition	900,000	300,000	800,000	300,000