Earnings Per Share (Computation Of Basic And Diluted Earnings Per Share) (Detail) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income (loss)	$ 45,000,000	$ 189,000,000	$ (594,000,000)	$ 160,000,000
Basic weighted average shares outstanding	69,700	75,200	70,800	75,600
Basic	$ 0.64	$ 2.52	$ (8.40)	$ 2.12
Diluted	$ 0.63	$ 2.50	$ (8.40)	$ 2.10
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted Average Number of Shares Outstanding, Diluted	70,200	75,700	70,800	76,200
Weighted Average Number Diluted Shares Outstanding Adjustment	500	500	0	600
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			1,400	500