Other Comprehensive (Loss) Income - Schedule of Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	$ (92.2)	$ 696.6	$ 620.4
Amounts reclassified from accumulated other comprehensive loss	(63.7)	52.7	8.9
Other comprehensive (loss) income	(47.3)	92.2	(20.8)
Balance	(202.9)	(92.2)	696.6
Changes in the Fair Value of Derivatives
Accumulated Other Comprehensive Income Loss [Line Items]
Balance			(0.1)
Other comprehensive income (loss) before reclassifications			0.0
Amounts reclassified from accumulated other comprehensive loss			0.1
Amounts reclassified from cumulative translation adjustment			0.0
Amounts reclassified due to disposition of an operating entity		0.0
Other comprehensive (loss) income			0.1
Changes in the Fair Value of Available-for-Sale Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	119.3
Other comprehensive income (loss) before reclassifications	(48.5)	119.3
Amounts reclassified from accumulated other comprehensive loss	(70.8)
Other comprehensive (loss) income	(119.3)	119.3
Balance		119.3
Pension and Other Postretirement Benefits Plan Cost
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(159.5)	(727.5)	(762.3)
Other comprehensive income (loss) before reclassifications	10.6	(42.7)	22.1
Amounts reclassified from accumulated other comprehensive loss	4.3	52.7	8.9
Amounts reclassified from cumulative translation adjustment			3.8
Amounts reclassified due to disposition of an operating entity		1.2
Other comprehensive (loss) income	14.9	11.2	34.8
Distribution to Donnelley Financial and LSC		556.8
Balance	(144.6)	(159.5)	(727.5)
Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(15.5)	(65.7)	(11.2)
Other comprehensive income (loss) before reclassifications	53.6	(37.1)	(67.6)
Amounts reclassified from accumulated other comprehensive loss	2.8	0.0
Amounts reclassified from cumulative translation adjustment			13.1
Amounts reclassified due to disposition of an operating entity		(0.7)
Other comprehensive (loss) income	56.4	(37.8)	(54.5)
Distribution to Donnelley Financial and LSC		88.0
Balance	40.9	(15.5)	(65.7)
AOCI Attributable to Parent
Accumulated Other Comprehensive Income Loss [Line Items]
Balance	(55.7)	(793.2)	(773.6)
Other comprehensive income (loss) before reclassifications	15.7	39.5	(45.5)
Amounts reclassified from accumulated other comprehensive loss	(63.7)	52.7	9.0
Amounts reclassified from cumulative translation adjustment			16.9
Amounts reclassified due to disposition of an operating entity		0.5
Other comprehensive (loss) income	(48.0)	92.7	(19.6)
Distribution to Donnelley Financial and LSC		644.8
Balance	$ (103.7)	$ (55.7)	$ (793.2)