Earnings Per Share (Computation Of Basic And Diluted 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
Earnings Per Share [Abstract]
Net income	$ 213	$ 245	$ 152	$ 141
Basic weighted average shares outstanding	78.8	82.6	80.1	84.1
Weighted Average Number Diluted Shares Outstanding Adjustment	0.7	1.4	0.9	1.4
Weighted Average Number of Shares Outstanding, Diluted	79.5	84.0	81.0	85.5
Basic	$ 2.71	$ 2.96	$ 1.90	$ 1.68
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Earnings Per Share, Diluted	$ 2.68	$ 2.91	$ 1.88	$ 1.65
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	0.5	0.7	0.2	0.8