Financial Statements of Parent Company Guarantor - Condensed Consolidating Balance Sheet (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 78.7		$ 86.3	$ 141.7	$ 141.7	$ 216.9
Accounts and notes receivable, net	422.1	$ 485.8	483.1
Inventories	366.6	355.3	356.9
Other current assets	129.2	116.1	114.5
Current assets held for sale	0.0	711.8	708.0
Total current assets	996.6		1,748.8
Property, plant and equipment, net	270.6		279.8
Other assets
Investments in subsidiaries	0.0		0.0
Goodwill	2,088.8		2,112.8
Intangibles, net	296.5		321.8
Long-term intercompany debt			0.0
Other non-current assets	153.5	136.0	180.9
Non-current assets held for sale	0.0	3,788.0	3,989.6
Total other assets	2,538.8		6,605.1
Total assets	3,806.0		8,633.7
Current liabilities
Accounts payable	275.1		321.5
Employee compensation and benefits	77.5		115.8
Other current liabilities	356.8	404.0	401.3
Current liabilities held for sale	0.0		360.8
Total current liabilities	709.4		1,199.4
Other liabilities
Long-term debt	779.9		1,440.7
Pension and other post-retirement compensation and benefits	107.9		96.4
Deferred tax liabilities	118.4	105.0	108.6
Other non-current liabilities	201.5		213.8
Non-current liabilities held for sale	0.0	$ 510.4	537.0
Total liabilities	1,917.1		3,595.9
Equity
Total equity	1,888.9		5,037.8	4,903.5		4,254.4
Total liabilities and equity	3,806.0		8,633.7
Parent Company Guarantor
Current assets
Cash and cash equivalents	0.1		0.0	0.1		0.0
Accounts and notes receivable, net	0.0		0.0
Inventories	0.0		0.0
Other current assets	3.3		10.8
Current assets held for sale			0.0
Total current assets	3.4		10.8
Property, plant and equipment, net	0.0		0.0
Other assets
Investments in subsidiaries	1,901.2		5,205.1
Goodwill	0.0		0.0
Intangibles, net	0.0		0.0
Long-term intercompany debt			0.0
Other non-current assets	53.9		2.2
Non-current assets held for sale			0.0
Total other assets	1,955.1		5,207.3
Total assets	1,958.5		5,218.1
Current liabilities
Accounts payable	2.0		1.4
Employee compensation and benefits	0.0		0.4
Other current liabilities	38.3		99.6
Current liabilities held for sale			0.0
Total current liabilities	40.3		101.4
Other liabilities
Long-term debt	0.0		48.4
Pension and other post-retirement compensation and benefits	0.0		0.0
Deferred tax liabilities	0.0		0.0
Other non-current liabilities	29.3		30.5
Non-current liabilities held for sale			0.0
Total liabilities	69.6		180.3
Equity
Total equity	1,888.9		5,037.8
Total liabilities and equity	1,958.5		5,218.1
Guarantor Subsidiaries
Current assets
Cash and cash equivalents	0.0		0.0	0.0		0.0
Accounts and notes receivable, net	0.0		0.0
Inventories	0.0		0.0
Other current assets	0.0		1.8
Current assets held for sale			0.0
Total current assets	0.0		1.8
Property, plant and equipment, net	0.0		0.0
Other assets
Investments in subsidiaries	1,867.4		5,109.6
Goodwill	0.0		0.0
Intangibles, net	0.0		0.0
Long-term intercompany debt			94.1
Other non-current assets	34.2		0.0
Non-current assets held for sale			0.0
Total other assets	1,901.6		5,203.7
Total assets	1,901.6		5,205.5
Current liabilities
Accounts payable	0.0		0.0
Employee compensation and benefits	0.0		0.0
Other current liabilities	0.4		0.4
Current liabilities held for sale			0.0
Total current liabilities	0.4		0.4
Other liabilities
Long-term debt	0.0		0.0
Pension and other post-retirement compensation and benefits	0.0		0.0
Deferred tax liabilities	0.0		0.0
Other non-current liabilities	0.0		0.0
Non-current liabilities held for sale			0.0
Total liabilities	0.4		0.4
Equity
Total equity	1,901.2		5,205.1
Total liabilities and equity	1,901.6		5,205.5
Subsidiary Issuer
Current assets
Cash and cash equivalents	3.2		0.0	51.0		0.0
Accounts and notes receivable, net	1.8		0.0
Inventories	0.0		0.0
Other current assets	1.3		1.6
Current assets held for sale			0.0
Total current assets	6.3		1.6
Property, plant and equipment, net	0.0		0.0
Other assets
Investments in subsidiaries	2,501.7		7,156.1
Goodwill	0.0		0.0
Intangibles, net	0.0		0.0
Long-term intercompany debt			614.0
Other non-current assets	579.6		0.0
Non-current assets held for sale			0.0
Total other assets	3,081.3		7,770.1
Total assets	3,087.6		7,771.7
Current liabilities
Accounts payable	0.0		0.0
Employee compensation and benefits	0.0		0.0
Other current liabilities	10.1		9.5
Current liabilities held for sale			0.0
Total current liabilities	10.1		9.5
Other liabilities
Long-term debt	1,210.3		2,652.8
Pension and other post-retirement compensation and benefits	0.0		0.0
Deferred tax liabilities	0.0		0.0
Other non-current liabilities	0.0		0.0
Non-current liabilities held for sale			0.0
Total liabilities	1,220.4		2,662.3
Equity
Total equity	1,867.2		5,109.4
Total liabilities and equity	3,087.6		7,771.7
Non-Guarantor Subsidiaries
Current assets
Cash and cash equivalents	75.4		86.3	90.6		216.9
Accounts and notes receivable, net	420.3		483.1
Inventories	366.6		356.9
Other current assets	128.3		109.5
Current assets held for sale			708.0
Total current assets	990.6		1,743.8
Property, plant and equipment, net	270.6		279.8
Other assets
Investments in subsidiaries	0.0		0.0
Goodwill	2,088.8		2,112.8
Intangibles, net	296.5		321.8
Long-term intercompany debt			(708.1)
Other non-current assets	610.4		2,159.4
Non-current assets held for sale			3,989.6
Total other assets	2,995.7		7,875.5
Total assets	4,256.9		9,899.1
Current liabilities
Accounts payable	273.1		320.1
Employee compensation and benefits	77.5		115.4
Other current liabilities	311.7		301.0
Current liabilities held for sale			360.8
Total current liabilities	662.3		1,097.3
Other liabilities
Long-term debt	694.2		720.2
Pension and other post-retirement compensation and benefits	107.9		96.4
Deferred tax liabilities	118.4		108.6
Other non-current liabilities	172.2		183.3
Non-current liabilities held for sale			537.0
Total liabilities	1,755.0		2,742.8
Equity
Total equity	2,501.9		7,156.3
Total liabilities and equity	4,256.9		9,899.1
Consolidation, Eliminations
Current assets
Cash and cash equivalents	0.0		0.0	$ 0.0		$ 0.0
Accounts and notes receivable, net	0.0		0.0
Inventories	0.0		0.0
Other current assets	(3.7)		(9.2)
Current assets held for sale			0.0
Total current assets	(3.7)		(9.2)
Property, plant and equipment, net	0.0		0.0
Other assets
Investments in subsidiaries	(6,270.3)		(17,470.8)
Goodwill	0.0		0.0
Intangibles, net	0.0		0.0
Long-term intercompany debt			0.0
Other non-current assets	(1,124.6)		(1,980.7)
Non-current assets held for sale			0.0
Total other assets	(7,394.9)		(19,451.5)
Total assets	(7,398.6)		(19,460.7)
Current liabilities
Accounts payable	0.0		0.0
Employee compensation and benefits	0.0		0.0
Other current liabilities	(3.7)		(9.2)
Current liabilities held for sale			0.0
Total current liabilities	(3.7)		(9.2)
Other liabilities
Long-term debt	(1,124.6)		(1,980.7)
Pension and other post-retirement compensation and benefits	0.0		0.0
Deferred tax liabilities	0.0		0.0
Other non-current liabilities	0.0		0.0
Non-current liabilities held for sale			0.0
Total liabilities	(1,128.3)		(1,989.9)
Equity
Total equity	(6,270.3)		(17,470.8)
Total liabilities and equity	$ (7,398.6)		$ (19,460.7)