Supplemental Cash Flow Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Open reverse repurchase commitments	$ 400,000,000.0	$ 0			$ 0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	43,400,000
Operating Lease, Payments	61,200,000
Income Taxes Paid	738,700,000	535,800,000
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	147,300,000	116,400,000
Cash and Cash Equivalents | ARX Holding Corp.
Open reverse repurchase commitments	62,800,000	$ 152,400,000			$ 117,300,000
Common Stock [Member] | Quarterly dividend [Member]
Dividends payable	$ 58,500,000		$ 58,400,000	$ 58,400,000