Net Income Per Share (Reconciliation Of Earnings Attributable To Common Shares Basic And Diluted) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Net income (loss)		$ 152	$ (266)	$ 802	$ (1,286)
Participating basic earnings	[1]	(1)	0	(6)	0
Basic earnings attributable to common stockholders		151	(266)	796	(1,286)
Reallocation of participating earnings		0	0	0	0
Diluted earnings attributable to common stockholders		$ 151	$ (266)	$ 796	$ (1,286)

[1] Unvested restricted stock awards represent participating securities because they participate in nonforfeitable dividends or distributions with the common equity holders of the Company. Participating earnings represent the distributed earnings of the Company attributable to the participating securities. Unvested restricted stock awards do not participate in undistributed net losses as they are not contractually obligated to do so.