Earnings Per Share (Computation Of Basic And Diluted Earnings Per Share) (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic earnings per share: [Abstract]
Net income (loss)	$ (146)	$ (1,229)	$ (244)	$ (1,301)
Net income (loss) available to common stockholders	$ (146)	$ (1,229)	$ (244)	$ (1,301)
Basic weighted average shares	89,131,760	125,653,189	88,865,272	128,511,897
Basic	$ (1.64)	$ (9.78)	$ (2.75)	$ (10.13)
Diluted earnings per share: [Abstract]
Net income (loss)	$ (146)	$ (1,229)	$ (244)	$ (1,301)
Net income (loss) available to common stockholders	$ (146)	$ (1,229)	$ (244)	$ (1,301)
Basic weighted average shares	89,131,760	125,653,189	88,865,272	128,511,897
Diluted weighted average shares	89,131,760	125,653,189	88,865,272	128,511,897
Diluted	$ (1.64)	$ (9.78)	$ (2.75)	$ (10.13)
Unvested Restricted Stock And Units That Receive Nonforfeitable Dividends Or Dividend Equivalents That Have Met Service Condition	800,000	300,000	800,000	300,000