Supplemental Cash Flow Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Open reverse repurchase commitments	$ 0	$ 0	$ 0
Income Taxes Paid	358,900,000	452,900,000
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	70,900,000	73,300,000
Cash and Cash Equivalents [Member] | ARX Holding Corp. [Member]
Open reverse repurchase commitments	$ 155,900,000	$ 130,200,000	$ 247,200,000