NET INCOME PER SHARE - Computation of Basic and Diluted Net Income Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share, Basic and Diluted [Abstract]
Net income	$ 123.7	$ 156.8	$ 272.0	$ 504.8
Weighted-average shares outstanding used in basic calculation	36.1	38.6	37.1	39.6
Add: Dilutive effect of potential common shares	0.8	0.7	0.8	0.9
Weighted-average shares used in computing diluted net income per share	36.9	39.3	37.9	40.5
Net income per share:
Basic (in dollars per share)	$ 3.43	$ 4.06	$ 7.33	$ 12.75
Diluted (in dollars per share)	$ 3.35	$ 3.99	$ 7.18	$ 12.46