Recent Accounting Pronouncements - Summary Of Information About In Adoption Of ASU 2019-12 (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2019	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Provision (benefit) for income taxes						$ 2	$ 0	$ 944
Net income (loss)						$ (359)	$ (296)	$ (1,605)
Earnings Per Share [Abstract]
Basic						$ (4.43)	$ (3.33)	$ (13.50)
Diluted						$ (4.43)	$ (3.33)	$ (13.50)
Previously Reported [Member] | Accounting Standards Update 2019-12 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Provision (benefit) for income taxes	$ 18	$ (37)	$ (2)	$ (39)	$ (21)
Net income (loss)	$ 71	$ (170)	$ (17)	$ (187)	$ (116)
Earnings Per Share [Abstract]
Basic	$ 0.86	$ (2.02)	$ (0.20)	$ (2.20)	$ (1.40)
Diluted	$ 0.86	$ (2.02)	$ (0.20)	$ (2.20)	$ (1.40)
Revised [Member] | Accounting Standards Update 2019-12 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Provision (benefit) for income taxes	$ 6	$ 0	$ 2	$ 2	$ 8
Net income (loss)	$ 83	$ (207)	$ (21)	$ (228)	$ (145)
Earnings Per Share [Abstract]
Basic	$ 1.00	$ (2.45)	$ (0.24)	$ (2.68)	$ (1.75)
Diluted	$ 1.00	$ (2.45)	$ (0.24)	$ (2.68)	$ (1.75)