Pension And Other Postretirement Benefit Plans (Narrative) (Detail) - Pension Plans, Defined Benefit - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year	$ 12.0
Defined Benefit Plan, Contributions by Employer	$ 5.4	$ 8.3