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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 245	$ 209	$ 141	$ 194
Basic weighted average shares outstanding	82.6	90.4	84.1	93.5
Weighted Average Number Diluted Shares Outstanding Adjustment	1.4	1.4	1.4	1.3
Weighted Average Number of Shares Outstanding, Diluted	84.0	91.8	85.5	94.8
Basic	$ 2.96	$ 2.32	$ 1.68	$ 2.07
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Document Fiscal Year Focus			2017
Diluted	$ 2.91	$ 2.28	$ 1.65	$ 2.05
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	0.7	0.2	0.8	0.2