Net Income Per Share (Reconciliation Of Earnings Attributable To Common Shares Basic And Diluted) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Earnings Per Share, Basic and Diluted, by Common Class, Including Two Class Method [Line Items]
Net income (loss)		$ 650	$ (1,020)
Participating basic earnings	[1]	(5)	0
Basic net income (loss) attributable to common stockholders		645	(1,020)
Reallocation of participating earnings		0	0
Diluted net income (loss) attributable to common stockholders		$ 645	$ (1,020)

[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.