Stockholders' Equity - Earnings Per Share Reconciliation (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net income (loss)
Net income (loss) attributable to common stockholders	$ (1,025)	$ 29	$ (1,040)	$ 150
Income (loss) effect of TEUs	0	(1)	0	(4)
Less distributions on participating securities	1	1	3	2
Basic	(1,026)	27	(1,043)	144
Income (loss) effect of TEUs	0	0	0	(1)
Diluted	$ (1,026)	$ 27	$ (1,043)	$ 143
Shares
Average number of common shares outstanding—basic (in shares)	491	504	491	511
Dilutive effect of stock options (in shares)	0	1	0	1
Average number of common shares outstanding—diluted (in shares)	491	505	491	512
Excluded due to anti-dilutive effect (in shares)	12	9	12	9
Net income (loss) per common share
Basic (in usd per share)	$ (2.09)	$ 0.05	$ (2.13)	$ 0.28
Diluted (in usd per share)	(2.09)	0.05	(2.13)	0.28
Dividends per common share (in usd per share)	$ 0.30	$ 0.25	$ 0.60	$ 0.50