Recent Accounting Pronouncements (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jan. 01, 2020	Dec. 31, 2019
Income Tax Expense (Benefit)	$ 0	$ 6	$ 0	$ 8
Net Income (Loss) Attributable to Parent	$ (58)	$ 83	$ (497)	$ (145)
Net income (loss) per basic common share	$ (1.11)	$ 1.00	$ (7.97)	$ (1.75)
Net income (loss) per diluted common share	$ (1.11)	$ 1.00	$ (7.97)	$ (1.75)
Retained Earnings (Accumulated Deficit)	$ 68		$ 68			$ 607
ASU 2016-13 [Member]
Retained Earnings (Accumulated Deficit)					$ 42
ASU 2019-12 [Member] | Previously Reported [Member]
Income Tax Expense (Benefit)		$ 18		$ (21)
Net Income (Loss) Attributable to Parent		$ 71		$ (116)
Net income (loss) per basic common share		$ 0.86		$ (1.40)
Net income (loss) per diluted common share		$ 0.86		$ (1.40)