Changes In Equity And Accumulated Other Comprehensive Loss (Summary Of Changes In Equity) (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	$ 1,423.6	$ 1,407.5	$ 1,476.3	$ 1,674.4	$ 1,593.0	$ 1,527.1	$ 1,476.3	$ 1,527.1
Net income	56.6	14.8	62.8	72.6	91.0	82.5	134.2	246.1
Cash dividends	(24.9)	(24.9)	(25.5)	(23.4)	(23.3)	(23.4)
Reacquisition on open market			(70.0)
Stock-based compensation expense	5.7	4.7	5.8	5.7	5.6	5.5
Deconsolidation of a joint venture						(0.5)
Changes in pension and postretirement plan assets and benefit obligation, net of tax	3.4	3.6	3.6	3.0	1.9	2.9	10.4	7.8
Currency translation adjustment	41.1	17.4	(45.5)	(33.7)	4.7	(0.9)
Balance, end of period	1,509.1	1,423.6	1,407.5	1,700.0	1,674.4	1,593.0	$ 1,509.1	$ 1,700.0
Impact from settlement of share-based awards, net of shares acquired	$ 3.6	$ 0.5	$ 0.0	$ 1.4	$ 1.5	$ (0.2)
Dividends per share (in dollars per share)	$ 0.43	$ 0.43	$ 0.43	$ 0.39	$ 0.39	$ 0.39	$ 1.29	$ 1.17
Reacquisition on open market (in shares)			1,221,233,000,000
Common Shares Issued at Par Value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	$ 72.4	$ 72.4	$ 72.4	$ 72.4	$ 72.4	$ 72.4	$ 72.4	$ 72.4
Balance, end of period	72.4	72.4	72.4	72.4	72.4	72.4	72.4	72.4
Capital Surplus
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	318.7	315.4	315.6	304.1	299.2	303.5	315.6	303.5
Stock-based compensation expense	5.7	4.7	5.8	5.7	5.6	5.5
Balance, end of period	324.5	318.7	315.4	310.1	304.1	299.2	324.5	310.1
Impact from settlement of share-based awards, net of shares acquired	0.1	(1.4)	(6.0)	0.3	(0.7)	(9.8)
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	2,139.4	2,149.5	2,112.2	2,198.8	2,131.1	2,072.1	2,112.2	2,072.1
Net income	56.6	14.8	62.8	72.5	91.0	82.4
Cash dividends	(24.9)	(24.9)	(25.5)	(23.4)	(23.3)	(23.4)
Balance, end of period	2,171.1	2,139.4	2,149.5	2,247.9	2,198.8	2,131.1	2,171.1	2,247.9
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(504.5)	(525.3)	(483.7)	(438.9)	(445.5)	(447.6)	(483.7)	(447.6)
Changes in pension and postretirement plan assets and benefit obligation, net of tax	3.4	3.6	3.6	3.0	1.9	2.9
Currency translation adjustment	41.0	17.2	(45.2)	(33.7)	4.7	(0.8)
Balance, end of period	(460.1)	(504.5)	(525.3)	(469.6)	(438.9)	(445.5)	(460.1)	(469.6)
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(604.9)	(606.8)	(542.8)	(464.4)	(466.6)	(476.2)	(542.8)	(476.2)
Reacquisition on open market			(70.0)
Balance, end of period	(601.4)	(604.9)	(606.8)	(463.3)	(464.4)	(466.6)	(601.4)	(463.3)
Impact from settlement of share-based awards, net of shares acquired	3.5	1.9	6.0	1.1	2.2	9.6
Total Shareholders’ Equity
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	1,421.1	1,405.2	1,473.7	1,672.0	1,590.6	1,524.2	1,473.7	1,524.2
Net income	56.6	14.8	62.8	72.5	91.0	82.4
Cash dividends	(24.9)	(24.9)	(25.5)	(23.4)	(23.3)	(23.4)
Reacquisition on open market			(70.0)
Stock-based compensation expense	5.7	4.7	5.8	5.7	5.6	5.5
Changes in pension and postretirement plan assets and benefit obligation, net of tax	3.4	3.6	3.6	3.0	1.9	2.9
Currency translation adjustment	41.0	17.2	(45.2)	(33.7)	4.7	(0.8)
Balance, end of period	1,506.5	1,421.1	1,405.2	1,697.5	1,672.0	1,590.6	1,506.5	1,697.5
Impact from settlement of share-based awards, net of shares acquired	3.6	0.5		1.4	1.5	(0.2)
Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	2.5	2.3	2.6	2.4	2.4	2.9	2.6	2.9
Net income				0.1		0.1
Deconsolidation of a joint venture						(0.5)
Currency translation adjustment	0.1	0.2	(0.3)	0.0	0.0	(0.1)
Balance, end of period	$ 2.6	$ 2.5	$ 2.3	$ 2.5	$ 2.4	$ 2.4	$ 2.6	$ 2.5