Summary Of Pre Tax Amounts Recognized In Other Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Pension And Other Retirement Benefits Recognized In Accumulated Other Comprehensive Income Loss [Line Items]
Amortization of prior service costs	$ 8.7	$ 9.7	$ 13.5
Net actuarial gains arising during period	20.9	0.3	18.5
Pension Plans [Member]
Schedule Of Pension And Other Retirement Benefits Recognized In Accumulated Other Comprehensive Income Loss [Line Items]
Amortization of net acturial losses	8.8	9.8	12.5
Amortization of prior service costs		0.1	0.7
Prior service costs			6.5
Net actuarial gains arising during period	21.1	0.8	8.4
Total recognized in OCI - pre-tax	29.9	10.7	28.1
Other Retirement Plans [Member]
Schedule Of Pension And Other Retirement Benefits Recognized In Accumulated Other Comprehensive Income Loss [Line Items]
Amortization of net acturial losses	0.1	0.2	0.3
Amortization of prior service costs	(0.3)	(0.3)
Prior service costs			1.2
Net actuarial gains arising during period	0.9	0.2	1.3
Total recognized in OCI - pre-tax	$ 0.7	$ 0.1	$ 2.8