Changes In Equity And Comprehensive Income (Summary Of Changes In Equity) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	$ 1,348.5	$ 1,145.7
Dividends	(20.9)	(19.6)
Exercise of stock options, net of shares reacquired	4.5	12.8
Stock compensation expense	5.6	5.6
Excess tax benefit from stock based compensation		0.0
Net income	68.7	63.3
Other comprehensive income (loss)	35.0	24.5
Comprehensive income	103.7	87.8
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest	0.0	0.4
Balance, end of period	1,448.1	1,232.3
Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	1,345.2	1,133.8
Dividends	(20.9)	(19.6)
Exercise of stock options, net of shares reacquired	4.5	12.8
Stock compensation expense	5.6	5.6
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	6.7
Excess tax benefit from stock based compensation		0.0
Net income	68.7	63.1
Other comprehensive income (loss)	35.0	24.3
Comprehensive income	103.7	87.4
Balance, end of period	1,444.8	1,220.0
Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	3.3	11.9
Net income	0.0	0.2
Other comprehensive income (loss)	0.0	0.2
Comprehensive income		0.4
Balance, end of period	$ 3.3	$ 12.3