Other Comprehensive (Loss) Income - Schedule of Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions		12 Months Ended
	Jul. 01, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Balance		$ (202.9)	$ (92.2)	$ 696.6
Amounts reclassified from accumulated other comprehensive loss		4.4	(63.7)	52.7
Other comprehensive (loss) income		(28.5)	(47.3)	92.2
Balance		(245.4)	(202.9)	(92.2)
Accounting Standards Update 2018 02
Accumulated Other Comprehensive Income Loss [Line Items]
Impact of adopting ASU 2018-02	$ 22.0
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 OPEB Plan Cost
Accumulated Other Comprehensive Income Loss [Line Items]
Balance		(144.6)	(159.5)	(727.5)
Other comprehensive income (loss) before reclassifications		6.4	10.6	(42.7)
Amounts reclassified from accumulated other comprehensive loss		4.4	4.3	52.7
Amounts reclassified due to disposition of an operating entity				1.2
Impact of adopting ASU 2018-02		(22.0)
Other		0.6
Other comprehensive (loss) income		11.4	14.9	11.2
Distribution to Donnelley Financial and LSC				556.8
Balance		(155.2)	(144.6)	(159.5)
Pension and OPEB Plan Cost | Accounting Standards Update 2018 02
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income		(10.6)
Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Balance		40.9	(15.5)	(65.7)
Other comprehensive income (loss) before reclassifications		(39.5)	53.6	(37.1)
Amounts reclassified from accumulated other comprehensive loss		0.0	2.8
Amounts reclassified due to disposition of an operating entity				(0.7)
Other comprehensive (loss) income			56.4	(37.8)
Distribution to Donnelley Financial and LSC				88.0
Balance		1.4	40.9	(15.5)
Translation Adjustments | Accounting Standards Update 2018 02
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income		(39.5)
AOCI Attributable to Parent
Accumulated Other Comprehensive Income Loss [Line Items]
Balance		(103.7)	(55.7)	(793.2)
Other comprehensive income (loss) before reclassifications		(33.1)	15.7	39.5
Amounts reclassified from accumulated other comprehensive loss		4.4	(63.7)	52.7
Amounts reclassified due to disposition of an operating entity				0.5
Impact of adopting ASU 2018-02		(22.0)
Other		0.6
Other comprehensive (loss) income			(48.0)	92.7
Distribution to Donnelley Financial and LSC				644.8
Balance		(153.8)	$ (103.7)	$ (55.7)
AOCI Attributable to Parent | Accounting Standards Update 2018 02
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income		$ (50.1)