Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income attributable to stockholders		$ 52	$ 103	$ 418	$ 2,565
Earnings allocated to participating securities			(1)	(1)	(7)
Net income attributable to stockholders net of earnings allocated to participating securities		$ 52	$ 102	$ 417	$ 2,558
Denominator:
Weighted average shares outstanding - basic		200	214	204	210
Unvested restricted shares		1	1	1
Net effect of shares issued with respect to E&P Dividend	[1]				4
Weighted average shares outstanding - diluted		201	215	205	214
Basic EPS	[2]	$ 0.26	$ 0.48	$ 2.04	$ 12.16
Diluted EPS	[2]	$ 0.26	$ 0.48	$ 2.04	$ 11.94

[1] Shares issued in connection with the distribution of our C corporation earnings and profits attributable to the period prior to spin-off (“E&P Dividend”).

[2] Per share amounts are calculated based on unrounded numbers and are calculated independently for each period presented; therefore, the sum of the quarterly EPS does not equal the EPS for the nine months.