Income Taxes - Reconciliation of Income Tax Expense at U.S. Federal Statutory Tax Rate (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
Income taxes at the U.S. federal statutory tax rate	$ (3.3)	$ 10.6	$ 0.3
Change in valuation allowances	(3.7)	8.1	8.3
Interest limitation valuation allowance	(8.0)	27.8	21.2
State and local income taxes, net of U.S. federal income tax benefit	4.7	(7.3)	(5.9)
Foreign tax	(2.1)	5.1	4.6
Adjustment of uncertain tax positions and interest	1.1	(0.6)	(5.4)
Foreign tax rate differential	(0.8)	(0.5)	(3.7)
Impact of the Tax Act			5.5
Tax impact of net gain on sale of Donnelley Financial and LSC shares		0.5
Tax impact on GILTI	3.5	5.2	4.9
Corporate owned life insurance policies	17.3
Other	1.3	6.0	1.7
Total	$ 10.0	$ 54.9	$ 31.5