WRKCo 10-K 20 Nov 17 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information Document - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Nov. 03, 2017	Mar. 31, 2017
Entity Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	WRK
Entity Registrant Name	WestRock CO
Entity Central Index Key	1,636,023
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		254,614,437
Entity Public Float			$ 13,240
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Well-known Seasoned Issuer	Yes

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Net sales	$ 14,859.7	$ 14,171.8	$ 11,124.8
Cost of goods sold	12,119.5	11,413.2	8,986.5
Gross profit	2,740.2	2,758.6	2,138.3
Selling, general and administrative, excluding intangible amortization	1,399.6	1,379.4	1,014.6
Selling, general and administrative intangible amortization	229.6	211.8	118.9
Pension risk transfer expense	0	370.7	0
Pension lump sum settlement and retiree medical curtailment, net	32.6	0	11.5
Land and Development impairment	46.7	0	0
Restructuring and other costs, net	196.7	366.4	140.8
Operating profit	835	430.3	852.5
Interest expense	(277.7)	(256.7)	(132.5)
Gain (loss) on extinguishment of debt	1.8	2.7	(2.6)
Interest income and other income (expense), net	66.7	58.6	9.7
Equity in income of unconsolidated entities	39	9.7	7.1
Gain on sale of HH&B	192.8	0	0
Income from continuing operations before income taxes	857.6	244.6	734.2
Income tax expense	(159)	(89.8)	(233)
Income from continuing operations	698.6	154.8	501.2
(Loss) income from discontinued operations (net of income tax benefit (expense) of $0, $32.3 and $(17.5)	0	(544.7)	10.6
Consolidated net income (loss)	698.6	(389.9)	511.8
Less: Net loss (income) attributable to noncontrolling interests	9.6	(6.4)	(4.7)
Net income (loss) attributable to common stockholders	$ 708.2	$ (396.3)	$ 507.1
Basic earnings per share from continuing operations	$ 2.81	$ 0.60	$ 2.92
Basic (loss) earnings per share from discontinued operations	0	(2.16)	0.05
Basic earnings (loss) per share attributable to common stockholders	2.81	(1.56)	2.97
Diluted earnings per share from continuing operations	2.77	0.59	2.87
Diluted (loss) earnings per share from discontinued operations	0	(2.13)	0.06
Diluted earnings (loss) per share attributable to common stockholders	2.77	(1.54)	2.93
Cash dividends paid per share	$ 1.60	$ 1.50	$ 1.20

Consolidated Statements of Inco

Consolidated Statements of Income (Parenthetical Information) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Discontinued Operation, Tax Effect of Discontinued Operation	$ 0	$ 32.3	$ (17.5)

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016		Sep. 30, 2015
Consolidated net income (loss)	$ 698.6	$ (389.9)		$ 511.8
Other comprehensive income (loss), net of tax:
Foreign currency translation gain (loss)	80.7	109.8		(242)
Reclassification adjustment of net loss on foreign currency translation included in earnings	0	20.2		0
Sale of HH&B	26.8	0		0
Derivatives:
Deferred loss on cash flow hedges	0	(0.4)		(1.6)
Reclassification adjustment of net (gain) loss on cash flow hedges included in earnings	(0.5)	1.2		0.4
Unrealized gain on available for sale security	0.7	0		0
Defined benefit pension and other postretirement benefit plans:
Net actuarial gain (loss) arising during period	22.2	(224.6)		(52.6)
Amortization and settlement recognition of net actuarial loss, included in pension and postretirement cost (1)	36	236.5	[1],[2]	30.3
Prior service credit (cost) arising during period	0.7	1.4		(15.4)
Amortization and curtailment recognition of prior service (credit) cost, included in pension and postretirement cost	(0.2)	1.1		(4.6)
Sale of HH&B	2.9	0		0
Other comprehensive income (loss)	169.3	145.2		(285.5)
Comprehensive income (loss)	867.9	(244.7)		226.3
Less: Comprehensive loss (income) attributable to noncontrolling interests	9.4	(5.7)		(3.9)
Comprehensive income (loss) attributable to common stockholders	$ 877.3	$ (250.4)		$ 222.4
[1]	Fiscal 2016 includes pension risk transfer expense, net of tax.
[2]	Includes pension risk transfer expense.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Sep. 30, 2017	Sep. 30, 2016
Current Assets:
Cash and cash equivalents		$ 298.1	$ 340.9
Restricted cash		5.9	25.5
Accounts receivable (net of allowances of $45.8 and $36.5)		1,886.8	1,592.2
Inventories		1,797.3	1,638.2
Other current assets		329.2	263.5
Assets held for sale		173.6	52.3
Total current assets		4,490.9	3,912.6
Property, plant and equipment, net		9,118.3	9,294.3
Goodwill		5,528.3	4,778.1
Intangibles, net		3,329.3	2,599.3
Restricted assets held by special purpose entities		1,287.4	1,293.8
Prepaid pension asset		368	257.8
Other assets		966.8	902.3
Assets		25,089	23,038.2
Current liabilities:
Current portion of debt		608.7	292.9
Accounts payable		1,492.1	1,054.4
Accrued compensation and benefits		416.7	405.9
Other current liabilities		492.3	429.8
Total current liabilities		3,009.8	2,183
Long-term debt due after one year		5,946.1	5,496.3
Pension liabilities, net of current portion		279.4	328.1
Postretirement benefit liabilities, net of current portion		153.4	140
Non-recourse liabilities held by special purpose entities		1,161.9	1,170.2
Deferred income taxes		3,410.2	3,130.7
Other long-term liabilities		737.4	746.2
Commitments and contingencies (Notes 13 and 19)
Redeemable noncontrolling interests		4.7	13.7
Equity:
Preferred stock, $0.01 par value; 30.0 million shares authorized; no shares outstanding		0	0
Common stock, $0.01 par value; 600.0 million shares authorized; 254.5 million and 251.0 million shares outstanding at September 30, 2017 and September 30, 2016, respectively		2.5	2.5
Capital in excess of par value		10,624.9	10,458.6
Retained earnings (deficit)		172.4	(105.9)
Accumulated other comprehensive loss	[1]	(457.3)	(626.4)
Total stockholders’ equity		10,342.5	9,728.8
Noncontrolling interests		43.6	101.2
Total equity		10,386.1	9,830
Total Liabilities and Equity		$ 25,089	$ 23,038.2
[1]	All amounts are net of tax and noncontrolling interest.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical Information) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Allowance for Doubtful Accounts Receivable, Current	$ 45.8	$ 36.5
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	30,000,000	30,000,000
Preferred Stock, Shares Outstanding	0	0
Class A Common Stock, par value	$ 0.01	$ 0.01
Common Stock, Shares Authorized	600,000,000	600,000,000
Common Stock, Shares, Outstanding	254,500,000	251,000,000

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) shares in Millions, $ in Millions		Total		Common Stock [Member]		Capital in Excess of Par Value [Member]		Retained Earnings [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Noncontrolling Interests [Member]		Smurfit Stone [Member]	Common Stock [Member]
Balance at beginning of fiscal year at Sep. 30, 2014													140
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under restricted stock plan													1.7
Issuance of common stock, net of stock received for minimum tax withholdings	[1],[2]												131.4
Purchases of common stock	[3]												(16.1)
Balance at end of fiscal year at Sep. 30, 2015													257
Balance at beginning of fiscal year at Sep. 30, 2014				$ 1.4
Balance at end of fiscal year at Sep. 30, 2015				2.6
Balance at beginning of fiscal year at Sep. 30, 2014						$ 2,839.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Income tax benefit (expense) from share-based plans						22.5
Compensation expense under share-based plans						50.2
Issuance of common stock, net of stock received for minimum tax withholdings				1.3	[2]	8,084.1	[2]	$ (26.4)
Purchases of common stock	[3]			(0.1)		(439.7)		(564.7)
Separation of Specialty Chemicals business						0		0	$ 0	$ 0	[4]
Purchases of Common Stock Excluding Merger Related Purchases		$ 336.7
Noncontrolling interests assumed in business combinations	[4]									159.3
Balance at end of fiscal year at Sep. 30, 2015						10,767.8
Balance at beginning of fiscal year at Sep. 30, 2014								1,960.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common stockholders		507.1						507.1
Dividends declared (per share - $1.60, $1.50 and $1.20)	[5]							(215.3)
Balance at beginning of fiscal year at Sep. 30, 2015								1,661.6
Balance at beginning of fiscal year at Sep. 30, 2014									(495.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss), net of tax		(285.5)							(284.9)	0.1	[4]
Balance at end of fiscal year at Sep. 30, 2015		(780.2)	[6]						(780.2)
Balance at beginning of fiscal year at Sep. 30, 2014	[4]									0.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income		(4.7)								0.7	[4]
Contributions	[4]									3.5
Distributions	[4]									(31.9)
Sale of subsidiary shares from noncontrolling interest	[4]									0
Balance at end of fiscal year at Sep. 30, 2015	[4]									132.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Fair value of share-based awards issued in business combinations						210.9
Total Stockholders’ equity		11,651.8
Total equity		$ 11,783.9
Shares issued under restricted stock plan													1.6
Issuance of common stock, net of stock received for minimum tax withholdings	[1],[2]												0.5
Purchases of common stock	[3]												(8.1)
Balance at end of fiscal year at Sep. 30, 2016		251											251
Balance at end of fiscal year at Sep. 30, 2016		$ 2.5		2.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Income tax benefit (expense) from share-based plans						(15.5)
Compensation expense under share-based plans						76
Issuance of common stock, net of stock received for minimum tax withholdings				0		13.9	[2]	(0.8)
Purchases of common stock	[3]			(0.1)		(319.2)		(16)
Separation of Specialty Chemicals business						(64.4)		(970.2)	7.9	(26.1)	[4]
Purchases of Common Stock Excluding Merger Related Purchases		335.3
Noncontrolling interests assumed in business combinations	[4]									10.9
Balance at end of fiscal year at Sep. 30, 2016						10,458.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common stockholders		(396.3)						(396.3)
Dividends declared (per share - $1.60, $1.50 and $1.20)	[5]							(384.2)
Balance at beginning of fiscal year at Sep. 30, 2016		(105.9)						(105.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss), net of tax		145.2							145.9	0	[4]
Balance at end of fiscal year at Sep. 30, 2016		(626.4)	[6]						(626.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income		(6.4)								3.2	[4]
Contributions	[4]									0
Distributions	[4]									(18.7)
Sale of subsidiary shares from noncontrolling interest	[4]									(0.2)
Balance at end of fiscal year at Sep. 30, 2016		101.2								101.2	[4]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Fair value of share-based awards issued in business combinations						0
Total Stockholders’ equity		9,728.8
Total equity		$ 9,830
Common Stock, Capital Shares Reserved for Future Issuance												0.3
Shares issued under restricted stock plan													1.1
Issuance of common stock, net of stock received for minimum tax withholdings	[1],[2]												4.2
Purchases of common stock	[3]												(1.8)
Balance at end of fiscal year at Sep. 30, 2017		254.5											254.5
Balance at end of fiscal year at Sep. 30, 2017		$ 2.5		2.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Income tax benefit (expense) from share-based plans						4.3
Compensation expense under share-based plans						60.6
Issuance of common stock, net of stock received for minimum tax withholdings				0	[2]	181.6	[2]	(5.9)
Purchases of common stock	[3]			$ 0		(76.3)		(16.7)
Separation of Specialty Chemicals business						(5.8)		0	0	0	[4]
Purchases of Common Stock Excluding Merger Related Purchases		93
Noncontrolling interests assumed in business combinations	[4]									0
Balance at end of fiscal year at Sep. 30, 2017						10,624.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to common stockholders		708.2						708.2
Dividends declared (per share - $1.60, $1.50 and $1.20)	[5]							(407.3)
Balance at beginning of fiscal year at Sep. 30, 2017		172.4						$ 172.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss), net of tax		169.3							169.1	0	[4]
Balance at end of fiscal year at Sep. 30, 2017		(457.3)	[6]						$ (457.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income		9.6								(12.9)	[4]
Contributions	[4]									0
Distributions	[4]									(44.7)
Sale of subsidiary shares from noncontrolling interest	[4]									0
Balance at end of fiscal year at Sep. 30, 2017		43.6								$ 43.6	[4]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Fair value of share-based awards issued in business combinations						$ 1.9
Total Stockholders’ equity		10,342.5
Total equity		$ 10,386.1
Common Stock, Capital Shares Reserved for Future Issuance												0.2
[1]	In connection with the Smurfit-Stone Acquisition, there were approximately 1.4 million shares reserved but unissued at the time of the acquisition for the resolution of Smurfit-Stone bankruptcy claims. At September 30, 2017, 0.2 million shares remain reserved and unissued.
[2]	Included in the Issuance of common stock in fiscal 2017 is the issuance of approximately 2.4 million shares of Common Stock valued at $136.1 million in connection with the U.S. Corrugated Acquisition. Included in the Issuance of common stock in fiscal 2015 is the issuance of approximately 131.2 million shares of Common Stock valued at $8,075.8 million in connection with the Combination.
[3]	In fiscal 2017, we repurchased approximately 1.8 million shares of our Common Stock for an aggregate cost of $93.0 million. In fiscal 2016, we repurchased approximately 8.1 million shares of our Common Stock for an aggregate cost of $335.3 million. Pursuant to the then existing repurchase plan, in the first quarter of fiscal 2015, RockTenn repurchased 0.2 million shares for an aggregate cost of $8.7 million. Subsequent to the Combination, in the fourth quarter of fiscal 2015, we repurchased approximately 5.4 million shares of our Common Stock for an aggregate cost of $328.0 million under the new authorization. Separately as part of the Combination, we repurchased 10.5 million shares of our Common Stock for an aggregate cost of $667.8 million.
[4]	Excludes amounts related to contingently redeemable noncontrolling interests, which are separately classified outside of permanent equity in the Consolidated Balance Sheets.
[5]	Includes cash dividends paid, dividend equivalent units on certain restricted stock awards and dividends declared but unpaid related to the shares reserved but unissued at the time of the acquisition for the resolution of Smurfit-Stone bankruptcy claims.
[6]	All amounts are net of tax and noncontrolling interest.

Consolidated Statements of Equ8

Consolidated Statements of Equity (Parenthetical Information) - USD ($) shares in Millions, $ in Millions

Jun. 09, 2017

Jul. 01, 2015

Sep. 30, 2015

Dec. 31, 2014

[1]

Sep. 30, 2017

Sep. 30, 2016

Sep. 30, 2015

Treasury Stock, Value, Acquired, Par Value Method

$ 328

$ 8.7

Purchases of Common Stock Excluding Merger Related Purchases

$ 93

$ 335.3

$ 336.7

Cash dividends paid per share

$ 1.60

$ 1.50

$ 1.20

Common Stock [Member]

Purchases of common stock

5.4

0.2

1.8

[1]

8.1

[1]

16.1

[1]

U.S. Corrugated [Member]

Business Combination, Consideration Transferred, Equity Interests Issued and Issuable

$ 136.1

Business Acquisition, Equity Interest Issued or Issuable, Number of Shares

2.4

MeadWestvaco [Member]

Purchases of Common Stock Excluding Merger Related Purchases

[1]

$ 667.8

Business Combination, Consideration Transferred, Equity Interests Issued and Issuable

$ 8,075.8

Business Acquisition, Equity Interest Issued or Issuable, Number of Shares

131.2

MeadWestvaco [Member] | Common Stock [Member]

Purchases of common stock

[1]

10.5

[1]

In fiscal 2017, we repurchased approximately 1.8 million shares of our Common Stock for an aggregate cost of $93.0 million. In fiscal 2016, we repurchased approximately 8.1 million shares of our Common Stock for an aggregate cost of $335.3 million. Pursuant to the then existing repurchase plan, in the first quarter of fiscal 2015, RockTenn repurchased 0.2 million shares for an aggregate cost of $8.7 million. Subsequent to the Combination, in the fourth quarter of fiscal 2015, we repurchased approximately 5.4 million shares of our Common Stock for an aggregate cost of $328.0 million under the new authorization. Separately as part of the Combination, we repurchased 10.5 million shares of our Common Stock for an aggregate cost of $667.8 million.

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Operating activities:
Consolidated net income (loss)	$ 698.6	$ (389.9)	$ 511.8
Adjustments to reconcile consolidated net income to net cash provided by operating activities:
Depreciation, depletion and amortization	1,116.6	1,146.5	740.8
Cost of real estate sold	207.9	87.7	32.1
Deferred income tax (benefit) expense	(20.4)	(160.9)	161.4
Share-based compensation expense	58	75.7	49.2
(Gain) loss on extinguishment of debt	(1.8)	(2.7)	2.6
(Gain) loss on disposal of plant, equipment and other, net	(4.9)	(6.5)	1
Equity in income of unconsolidated entities	(39)	(9.7)	(7.1)
Pension and other postretirement funding (more) than expense (income)	(51)	275.6	(137.7)
Gain on sale or deconsolidation of subsidiaries	(5)	0	0
Gain on Grupo Gondi investment	0	(12.1)	0
Gain on sale of HH&B	(192.8)	0	0
Cash surrender value increase in excess of premiums paid	(34)	(27.6)	0
Impairment adjustments	56.8	200.8	6.9
Distributed earnings from equity investments	26.9	9	0
Other non-cash items	(38.9)	(42.1)	(14.5)
Land and Development impairment	46.7	0	0
Impairment of Specialty Chemicals goodwill and intangibles	0	579.4	0
Change in operating assets and liabilities, net of acquisitions and divestitures:
Accounts receivable	(97.9)	36.6	106.1
Inventories	(48.2)	50.6	(27.2)
Other assets	(33.7)	(92.7)	(10)
Accounts payable	302.2	(197.1)	(38.4)
Income taxes	(67.1)	73.2	(23.6)
Accrued liabilities and other	21.5	94.6	(149.8)
Net cash provided by operating activities	1,900.5	1,688.4	1,203.6
Investing activities:
Capital expenditures	(778.6)	(796.7)	(585.5)
Cash (paid) received for purchase of businesses, net of cash acquired	(1,588.5)	(376.4)	3.7
Debt purchased in connection with an acquisition	0	(36.5)	0
Cash received in merger	0	0	265.7
Corporate-owned life insurance premium paid	(4.4)	(9)	0
Investment in unconsolidated entities	(2.5)	(179.9)	0
Cash Divested from Deconsolidation	(3.6)	0	0
Return of capital from unconsolidated entities	18.5	5.7	1.1
Cash received from affiliated entities	0	0	3.5
Proceeds from sale of subsidiary and affiliates	14.8	10.2	0
Proceeds from sale of HH&B	1,005.9	0	0
Proceeds from sale of property, plant and equipment	52.6	31.2	28.8
Net cash used for investing activities	(1,285.8)	(1,351.4)	(282.7)
Financing activities:
Proceeds from issuance of notes	998.4	0	0
Additions (repayments) to revolving credit facilities	421.8	125.5	(48.1)
Additions to debt	742.6	1,511.8	2,176.3
Repayments of debt	(2,331.9)	(1,073.3)	(1,587.5)
Other financing additions (repayments)	23.9	53.3	(0.6)
Debt issuance costs	(9.8)	(3.6)	(7.8)
Specialty Chemicals spin-off of net cash and trust funding	0	(105)	0
Issuances of common stock, net of related minimum tax withholdings	35.8	11.8	(19.3)
Purchases of common stock	(93)	(335.3)	(336.7)
Purchases of common stock - merger related	0	0	(667.8)
Excess tax benefits from share-based compensation	6.7	0.3	23
Payment for Contingent Consideration Liability, Financing Activities	(1.1)	0	0
Advances from (repayments to) unconsolidated entity	1.4	(2.3)	(0.3)
Cash dividends paid to stockholders	(403.2)	(380.7)	(214.5)
Cash distributions paid to noncontrolling interests	(47)	(33.5)	(34.7)
Net cash used for financing activities	(655.4)	(231)	(718)
Effect of exchange rate changes on cash and cash equivalents	(2.1)	6.6	(7.2)
(Decrease) Increase in cash and cash equivalents	(42.8)	112.6	195.7
Cash and cash equivalents from continuing operations, at beginning of period	340.9	207.8	32.6
Cash and cash equivalents from discontinued operations, at beginning of period	0	20.5	0
Balance of cash and cash equivalents at beginning of period	340.9	228.3	32.6
Cash and cash equivalents from continuing operations, at end of period	298.1	340.9	207.8
Cash and cash equivalents from discontinued operations, at end of period	0	0	20.5
Balance of cash and cash equivalents at end of period	298.1	340.9	228.3
Supplemental disclosure of cash flow information:
Income taxes, net of refunds	227.6	157.4	89.3
Interest, net of amounts capitalized	$ 239	$ 229.9	$ 140.1

Consolidated Statements of Ca10

Consolidated Statements of Cash Flows (Parenthetical Information) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Fair value of assets acquired, including goodwill		$ 3,342.4	$ 580.7	$ 16,001.1
Cash consideration for the purchase of businesses, net of cash acquired	[1]	(1,592)	(376.4)	0
Unreceived working capital or escrow		4.6	3.5	0
Debt purchased in connection with an acquisition		0	(36.5)	0
Stock issued in business combinations		(136.1)	0	(8,075.8)
Fair value of share-based awards issued in business combinations		(1.9)	0	(210.9)
Total liabilities and noncontrolling interests assumed		1,617	171.3	7,714.4
Debt assumed in acquisition		929.1	15	2,152.9
Noncash, Accounts Receivable		14.6	34.7
Noncash, Inventories		7.6	25.8
Noncash, Other Assets		12.3	86.3
Noncash, Accounts Payable		(7.9)	(15.4)
Noncash, Income Taxes		(1.4)	(1)
Noncash, Accrued Liabilities and Other		(12)	(18.8)
Noncash, Investment in Unconsolidated Entities		(16.7)	(123.7)
Equity Method Investments		360.6	$ 328.9	$ 60.2
Packaging Acquisition [Member]
Collection of Escrow Receivable in Business Combination		$ 3.5
[1]	The fiscal 2017 amount is different from the consolidated statements of cash flows line item “cash (paid) received for the purchase of businesses, net of cash acquired” as the statement of cash flow amount is net of the receipt of a $3.5 million escrow payment related to the Packaging Acquisition.

Description of Business and Sum

Description of Business and Summary of Significant Accounting Policies	12 Months Ended
	Sep. 30, 2017
Description of Business and Summary of Significant Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies [Text Block]	Description of Business and Summary of Significant Accounting Policies Description of Business Unless the context otherwise requires, “we” , “us” , “our” , “WestRock” and “the Company” refer to the business of WestRock Company, its wholly-owned subsidiaries and its partially-owned consolidated subsidiaries. WestRock is a multinational provider of paper and packaging solutions for consumer and corrugated packaging markets. We partner with our customers to provide differentiated paper and packaging solutions that help them win in the marketplace. Our team members support customers around the world from our operating and business locations in North America, South America, Europe, Asia and Australia. We also sell real estate primarily in the Charleston, SC region. WestRock was formed on March 6, 2015 for the purpose of effecting the Combination and, prior to the Combination, did not conduct any activities other than those incidental to its formation and the matters contemplated by the Business Combination Agreement. On July 1, 2015, pursuant to the Business Combination Agreement, RockTenn and MWV completed a strategic combination of their respective businesses and RockTenn and MWV each became wholly-owned subsidiaries of WestRock. RockTenn was the accounting acquirer in the Combination. We believe the Combination combined two industry leaders to create a leading global provider of consumer and corrugated packaging solutions. See “ Note 6. Merger, Acquisitions and Investment ” for additional information. On May 15, 2016, WestRock completed the Separation, pursuant to which we disposed of our former Specialty Chemicals segment in its entirety and ceased to consolidate its assets, liabilities and results of operations in our consolidated financial statements. Accordingly, we have presented the financial position and results of operations of our former Specialty Chemicals segment as discontinued operations in the accompanying consolidated financial statements for all periods presented. See “ Note 7. Discontinued Operations ” for additional information. On April 6, 2017, we completed the HH&B Sale. We used the proceeds from the HH&B Sale in connection with the MPS Acquisition. We recorded a pre-tax gain on sale of HH&B of $192.8 million in fiscal 2017. See “ Note 8. Assets Held For Sale ” for additional information. On June 6, 2017, we completed the MPS Acquisition. MPS is a global provider of print-based specialty packaging solutions and its differentiated product offering includes premium folding cartons, inserts, labels and rigid packaging. MPS is reported in our Consumer Packaging segment. See “ Note 6. Merger, Acquisitions and Investment ” for additional information. Consolidation The consolidated financial statements include our accounts and the accounts of our partially-owned consolidated subsidiaries. Equity investments in which we exercise significant influence but do not control and are not the primary beneficiary are accounted for using the equity method. Investments in which we are not able to exercise significant influence over the investee are accounted for under the cost method. Our equity and cost method investments are not significant either individually or in the aggregate. We have eliminated all significant intercompany accounts and transactions. See “ Note 21. Segment Information ” for our equity method investments. Reclassifications In fiscal 2017, we reported assets held for sale separately on our consolidated balance sheet, as well as distributed earnings from equity investments on our consolidated statements of cash flows. The presentation of other current assets on our consolidated balance sheets and other assets on our consolidated statements of cash flows at and for the year ended September 30, 2016 has been changed to conform to the current year presentation. In addition, due to the retrospective adoption of certain provisions of ASU 2015-07 “ Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share ” that eliminated the requirement to categorize within the fair value hierarchy investments for which fair value is measured using the net asset value (or its equivalent) practical expedient, we have conformed the September 30, 2016 table that summarizes our pension plan assets measured at fair value to the current year presentation and correspondingly removed the table that reflected changes in our level 3 pension plan assets since we had no level 3 assets remaining after the adoption. Use of Estimates Preparing consolidated financial statements in conformity with GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates, and the differences could be material. The most significant accounting estimates inherent in the preparation of our consolidated financial statements include estimates to evaluate the recoverability of goodwill, intangibles and property, plant and equipment, to determine the useful lives of assets that are amortized or depreciated, and to measure income taxes, self-insured obligations, restructuring activities and allocate the purchase price of an acquired business to the fair value of acquired assets and liabilities. In addition, significant estimates form the basis for our reserves with respect to collectibility of accounts receivable, inventory valuations, pension benefits, deferred tax asset valuation allowances and certain benefits provided to current and retired employees. Various assumptions and other factors underlie the determination of these significant estimates. The process of determining significant estimates is fact specific and takes into account factors such as historical experience, current and expected economic conditions, product mix, and in some cases, actuarial techniques. We regularly evaluate these significant factors and make adjustments where facts and circumstances dictate. Revenue Recognition We recognize revenue when there is persuasive evidence that an arrangement exists, delivery has occurred or services have been rendered, our price to the buyer is fixed or determinable and collectibility is reasonably assured. Delivery is not considered to have occurred until the customer takes title and assumes the risks and rewards of ownership. The timing of revenue recognition is dependent on the location of title transfer which is normally either on the exit from our plants (i.e., shipping point) or on arrival at customers’ plants (i.e., destination point). We do not recognize revenue from transactions where we bill customers, but retain custody and title to these products until the date custody and title transfer. We do not have any significant multiple deliverable revenue arrangements. We net, against our gross sales, provisions for discounts, returns, allowances, customer rebates and other adjustments. We account for such provisions during the same period in which we record the related revenues. We include in net sales any amounts related to shipping and handling that are billed to a customer. Shipping and Handling Costs We classify shipping and handling costs as a component of cost of goods sold. Cash Equivalents We consider all highly liquid investments that mature three months or less from the date of purchase to be cash equivalents. The carrying amounts we report in the consolidated balance sheets for cash and cash equivalents approximate fair market values. We place our cash and cash equivalents with large credit worthy banks, which limits the amount of our credit exposure. Accounts Receivable and Allowances We perform periodic evaluations of our customers’ financial condition and generally do not require collateral. The weighted average of our receivables collection is within 30 to 60 days. We sell certain receivables under our A/R Sales Agreement. We serve a diverse customer base primarily in North America, South America, Europe, Asia and Australia, and, therefore, have limited exposure from credit loss to any particular customer or industry segment. We state accounts receivable at the amount owed by the customer, net of an allowance for estimated uncollectible accounts, returns and allowances, cash discounts and other adjustments. We do not discount accounts receivable because we generally collect accounts receivable over a relatively short time. We account for sales and other taxes that are imposed on and concurrent with individual revenue-producing transactions between a customer and us on a net basis which excludes the taxes from our net sales. We estimate our allowance for doubtful accounts based on our historical experience, current economic conditions and the credit worthiness of our customers. We charge off receivables when they are determined to be no longer collectible. In fiscal 2017 , 2016 and 2015 our bad debt expense was not significant. The following table represents a summary of the changes in the reserve for allowance for doubtful accounts, returns and allowances and cash discounts for fiscal 2017 , 2016 and 2015 (in millions): 2017 2016 2015 Balance at beginning of fiscal year $ 36.5 $ 29.5 $ 25.1 Reduction in sales and charges to costs and expenses 215.6 200.8 166.6 Deductions (206.3 ) (193.8 ) (162.2 ) Balance at end of fiscal year $ 45.8 $ 36.5 $ 29.5 Inventories We value substantially all U.S. inventories at the lower of cost or market, with cost determined on the LIFO basis. We value all other inventories at the lower of cost or market, with cost determined using methods that approximate cost computed on a FIFO basis. These other inventories represent primarily foreign inventories, spare parts inventories and certain inventoried supplies and aggregate to approximately 32% and 35% of FIFO cost of all inventory at September 30, 2017 and 2016 , respectively. Prior to the application of the LIFO method, our U.S. operating divisions use a variety of methods to estimate the FIFO cost of their finished goods inventories. Such methods include standard costs, or average costs computed by dividing the actual cost of goods manufactured by the tons produced and multiplying this amount by the tons of inventory on hand. Lastly, certain operations calculate a ratio, on a plant by plant basis, the numerator of which is the cost of goods sold and the denominator is net sales. This ratio is applied to the estimated sales value of the finished goods inventory. Variances and other unusual items are analyzed to determine whether it is appropriate to include those items in the value of inventory. Examples of variances and unusual items that are considered to be current period charges include, but are not limited to, abnormal production levels, freight, handling costs, and wasted materials (spoilage). Cost includes raw materials and supplies, direct labor, indirect labor related to the manufacturing process and depreciation and other factory overheads. Our inventoried spare parts are measured at average cost. Property, Plant and Equipment We state property, plant and equipment at cost. Cost includes major expenditures for improvements and replacements that extend useful lives, increase capacity, increase revenues or reduce costs. During fiscal 2017 , 2016 and 2015 , we capitalized interest of approximately $7.0 million , $7.6 million and $4.0 million , respectively. For financial reporting purposes, we provide depreciation and amortization primarily on a straight-line method generally over the estimated useful lives of the assets as follows: Buildings and building improvements 15-40 years Machinery and equipment 3-25 years Transportation equipment 3-8 years Generally, our machinery and equipment have estimated useful lives between 3 and 25 years; however, select portions of machinery and equipment primarily at our mills have estimated useful lives up to 44 years. Greater than 90% of the cost of our mill assets have lives of 25 years or less. Leasehold improvements are depreciated over the shorter of the asset life or the lease term, generally between 3 and 10 years. Goodwill and Long-Lived Assets We review the carrying value of our goodwill annually at the beginning of the fourth quarter of each fiscal year, or more often if events or changes in circumstances indicate that the carrying amount may exceed fair value as set forth in ASC 350, “Intangibles — Goodwill and Other.” See “ Note 7. Discontinued Operations ” for information on the first quarter of fiscal 2016 goodwill impairment test and resulting charge. We test goodwill for impairment at the reporting unit level, which is an operating segment or one level below an operating segment, referred to as a component. A component of an operating segment is a reporting unit if the component constitutes a business for which discrete financial information is available and segment management regularly reviews the operating results of that component. However, two or more components of an operating segment are aggregated and deemed a single reporting unit if the components have similar economic characteristics. The amount of goodwill acquired in a business combination that is assigned to one or more reporting units as of the acquisition date is the excess of the purchase price of the acquired businesses (or portion thereof) included in the reporting unit, over the fair value assigned to the individual assets acquired or liabilities assumed. Goodwill is assigned to the reporting unit(s) expected to benefit from the synergies of the combination even though other assets or liabilities of the acquired entity may not be assigned to that reporting unit. We determine recoverability by comparing the estimated fair value of the reporting unit to which the goodwill applies to the carrying value, including goodwill, of that reporting unit using a discounted cash flow model. Prior to the adoption of ASU 2017-04, “ Simplifying the Test for Goodwill Impairment ”, the goodwill impairment model is a two-step process. We have not yet adopted the ASU. An amendment to ASC 350 became effective December 2011 that allows a qualitative assessment, prior to step one, to determine whether it is more likely than not that the fair value of a reporting unit exceeds its carrying amount. We did not attempt a qualitative assessment and moved directly to step one. In step one, we utilize the present value of expected net cash flows to determine the estimated fair value of our reporting units. This present value model requires management to estimate future net cash flows, the timing of these cash flows, and a discount rate (based on a weighted average cost of capital), which represents the time value of money and the inherent risk and uncertainty of the future cash flows. Factors that management must estimate when performing this step in the process include, among other items, sales volume, prices, inflation, discount rates, exchange rates, tax rates, anticipated synergies and productivity improvements resulting from acquisitions, capital expenditures and continuous improvement projects. The assumptions we use to estimate future cash flows are consistent with the assumptions that the reporting units use for internal planning purposes, updated to reflect current expectations. If we determine that the estimated fair value of the reporting unit exceeds its carrying amount, goodwill of the reporting unit is not impaired. If we determine that the carrying amount of the reporting unit exceeds its estimated fair value, we would complete step two of the impairment analysis. Step two involves determining the implied fair value of the reporting unit’s goodwill and comparing it to the carrying amount of that goodwill. If the carrying amount of the reporting unit’s goodwill exceeds the implied fair value of that goodwill, we recognize an impairment loss in an amount equal to that excess. During the fourth quarter of fiscal 2017 , of those reporting units that have goodwill, our Consumer Packaging and Brazil Corrugated reporting units had a fair value which exceeded their carrying value by a little more than 10%, due primarily to the Combination and the MPS Acquisition and the corresponding fair value accounting. If we had concluded that it was appropriate to increase the discount rate we used by 100 basis point to estimate the fair value of each reporting unit that has goodwill, the fair value for each of our reporting units would have continued to exceed its carrying value except for the Consumer Packaging and Brazil Corrugated reporting units. No events have occurred since the latest annual goodwill impairment assessment that would necessitate an interim goodwill impairment assessment. We follow the provisions included in ASC 360, “Property, Plant and Equipment” in determining whether the carrying value of any of our long-lived assets, including amortizing intangibles other than goodwill, is impaired. The ASC 360 test is a three-step test for assets that are “held and used” as that term is defined by ASC 360. We determine whether indicators of impairment are present. We review long-lived assets for impairment when events or changes in circumstances indicate that the carrying amount of the long-lived asset might not be recoverable. If we determine that indicators of impairment are present, we determine whether the estimated undiscounted cash flows for the potentially impaired assets are less than the carrying value. This requires management to estimate future net cash flows through operations over the remaining useful life of the asset and its ultimate disposition. The assumptions we use to estimate future cash flows are consistent with the assumptions we use for internal planning purposes, updated to reflect current expectations. If our estimated undiscounted cash flows do not exceed the carrying value, we estimate the fair value of the asset and record an impairment charge if the carrying value is greater than the fair value of the asset. We estimate fair value using discounted cash flows, observable prices for similar assets, or other valuation techniques. We record assets classified as “held for sale” at the lower of their carrying value or estimated fair value less anticipated costs to sell. Included in our long-lived assets are certain identifiable intangible assets. These intangible assets are amortized based on the approximate pattern in which the economic benefits are consumed or straight-line if the pattern was not reliably determinable. Estimated useful lives range from 1 to 40 years and have a weighted average life of approximately 16.6 years. Our judgments regarding the existence of impairment indicators are based on legal factors, market conditions and operational performance. Future events could cause us to conclude that impairment indicators exist and that assets associated with a particular operation are impaired. Evaluating impairment also requires us to estimate future operating results and cash flows, which also require judgment by management. Any resulting impairment loss could have a material adverse impact on our financial condition and results of operations. Restructuring Our restructuring and other costs, net include primarily items such as restructuring portions of our operations, acquisition costs, divestiture costs and integration costs. We have restructured portions of our operations from time to time, have current restructuring initiatives taking place, and it is possible that we may engage in future restructuring activities. Identifying and calculating the cost to exit these operations requires certain assumptions to be made, the most significant of which are anticipated future liabilities, including severance costs, leases and other contractual obligations, and the adjustment of property, plant and equipment to net realizable value. We believe our estimates are reasonable, considering our knowledge of the industries we operate in, previous experience in exiting activities and valuations we may obtain from independent third parties. Although our estimates have been reasonably accurate in the past, significant judgment is required, and these estimates and assumptions may change as additional information becomes available and facts or circumstances change. Business Combinations From time to time, we may enter into business combinations. In accordance with ASC 805, “ Business Combinations ”, we generally recognize the identifiable assets acquired, the liabilities assumed, and any noncontrolling interests in an acquiree at their fair values as of the date of acquisition. We measure goodwill as the excess of consideration transferred, which we also measure at fair value, over the net of the acquisition date fair values of the identifiable assets acquired and liabilities assumed. The acquisition method of accounting requires us to make significant estimates and assumptions regarding the fair values of the elements of a business combination as of the date of acquisition, including the fair values of identifiable intangible assets, deferred tax asset valuation allowances, liabilities including those related to debt, pensions and other postretirement plans, uncertain tax positions, contingent consideration and contingencies. This method also requires us to refine these estimates over a measurement period not to exceed one year to reflect new information obtained about facts and circumstances that existed as of the acquisition date that, if known, would have affected the measurement of the amounts recognized as of that date. If we are required to adjust provisional amounts that we have recorded for the fair values of assets and liabilities in connection with acquisitions, these adjustments could have a material impact on our financial condition and results of operations. Significant estimates and assumptions in estimating the fair value of acquired technology, customer relationships, and other identifiable intangible assets include future cash flows that we expect to generate from the acquired assets. If the subsequent actual results and updated projections of the underlying business activity change compared with the assumptions and projections used to develop these values, we could record impairment charges. In addition, we have estimated the economic lives of certain acquired assets and these lives are used to calculate depreciation and amortization expense. If our estimates of the economic lives change, depreciation or amortization expenses could be increased or decreased, or the acquired asset could be impaired. Fair Value of Financial Instruments and Nonfinancial Assets and Liabilities We estimate fair values in accordance with ASC 820 “Fair Value Measurement. ” We define fair value as the price that would be received from the sale of an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Financial instruments not recognized at fair value on a recurring or nonrecurring basis include cash and cash equivalents, accounts receivables, certain other current assets, short-term debt, accounts payable, certain other current liabilities and long-term debt. With the exception of long-term debt, the carrying amounts of these financial instruments approximate their fair values due to their short maturities. The fair values of our long-term debt are estimated using quoted market prices or are based on the discounted value of future cash flows. We disclose the fair value of long-term debt in “Note 11. Debt” and our pension and postretirement assets and liabilities in “Note 15. Retirement Plans” . We have, or from time to time may have, financial instruments recognized at fair value including Supplemental Plans that are nonqualified deferred compensation plans pursuant to which assets are invested primarily in mutual funds, interest rate derivatives, commodity derivatives or other similar class of assets or liabilities, the fair value of which are not significant. We measure the fair value of our mutual fund investments based on quoted prices in active markets, and our derivative contracts, if any, based on discounted cash flows. We measure certain nonfinancial assets and nonfinancial liabilities at fair value on a nonrecurring basis. These assets and liabilities include cost and equity method investments when they are deemed to be other-than-temporarily impaired, assets acquired and liabilities assumed in a merger or an acquisition or in a nonmonetary exchange, and property, plant and equipment and goodwill and other intangible assets that are written down to fair value when they are held for sale or determined to be impaired. Given the nature of nonfinancial assets and liabilities, evaluating their fair value from the perspective of a market participant is inherently complex. Assumptions and estimates about future values can be affected by a variety of internal and external factors. Changes in these factors may require us to revise our estimates and could result in future impairment charges for goodwill and acquired intangible assets, or retroactively adjust provisional amounts that we have recorded for the fair values of assets and liabilities in connection with business combinations. These adjustments could have a material impact on our financial condition and results of operations. We discuss fair values in more detail in “Note 12. Fair Value” . Derivatives We are exposed to interest rate risk, commodity price risk and foreign currency exchange risk. To manage these risks, from time to time and to varying degrees, we may enter into a variety of financial derivative transactions and certain physical commodity transactions that are determined to be derivatives. Interest rate swaps may be entered into to manage the interest rate risk associated with a portion of our outstanding debt. Interest rate swaps are either designated for accounting purposes as cash flow hedges of forecasted floating interest payments on variable rate debt or fair value hedges of fixed rate debt, or we may elect not to treat them as accounting hedges. Swaps or forward contracts on certain commodities may be entered into to manage the price risk associated with forecasted purchases or sales of those commodities. In addition, certain commodity financial derivative contracts and physical commodity contracts that are determined to be derivatives may not be designated as accounting hedges because either they do not meet the criteria for treatment as accounting hedges under ASC 815, “Derivatives and Hedging”, or we elect not to treat them as accounting hedges under ASC 815. We may also enter into forward contracts to manage our exposure to fluctuations in foreign currency rates with respect to transactions denominated in currencies such as Canadian dollars, the Euro or Brazilian Real. These also can either be designated for accounting purposes as cash flow hedges or not so designated. Outstanding financial derivative instruments expose us to credit loss in the event of nonperformance by the counterparties to the derivative agreements. Our credit exposure related to these financial instruments is represented by the fair value of contracts reported as assets. We manage our exposure to counterparty credit risk through minimum credit standards, diversification of counterparties and procedures to monitor concentrations of credit risk. We may enter into financial derivative contracts that may contain credit-risk-related contingent features which could result in a counterparty requesting immediate payment or demanding immediate and ongoing full overnight collateralization on derivative instruments in net liability positions. For financial derivative instruments that are designated as a cash flow hedge for accounting purposes, the effective portion of the gain or loss on the financial derivative instrument is reported as a component of other comprehensive income and reclassified into earnings in the same line item associated with the forecasted transaction, and in the same period or periods during which the forecasted transaction affects earnings. Gains and losses on the financial derivative representing either hedge ineffectiveness or hedge components excluded from the assessment of effectiveness are recognized in current earnings. We have at times entered into interest rate swap agreements that effectively modified our exposure to interest rate risk by converting a portion of our interest payments on floating rate debt to a fixed rate basis, thus reducing the impact of interest rate changes on future interest expense. These agreements typically involved the receipt of floating rate amounts in exchange for fixed interest rate payments over the life of the agreements without an exchange of the underlying principal amount. At September 30, 2017 , there were no interest rate or commodity derivatives outstanding, and the notional amount of foreign currency derivatives were $ 47.8 million . At September 30, 2016 , there were no foreign currency, interest rate or commodity derivatives outstanding. Health Insurance We are self-insured for the majority of our group health insurance costs. However, we seek to limit our health insurance costs by entering into certain stop loss insurance coverage. Due to mergers, acquisitions and other factors, we may have plans that do not include stop loss insurance. We calculate our group health insurance reserve on an undiscounted basis based on estimated reserve rates. We utilize claims lag data provided by our claims administrators to compute the required estimated reserve rate. We calculate our average monthly claims paid using the actual monthly payments during the trailing 12-month period. At that time, we also calculate our required reserve using the reserve rates discussed above. While we believe that our assumptions are appropriate, significant differences in our actual experience or significant changes in our assumptions may materially affect our group health insurance costs. Workers’ Compensation We purchase large risk deductible workers’ compensation policies for the majority of our workers’ compensation liabilities that are subject to various deductibles to limit our exposure. We calculate our workers’ compensation reserves on an undiscounted basis based on estimated actuarially calculated development factors. While we believe that our assumptions are appropriate, significant differences in our actual experience or significant changes in our assumptions may materially affect our workers' compensation costs. Income Taxes We account for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial statement carrying amount and the tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. All deferred tax assets and liabilities are classified as noncurrent in our consolidated balance sheet in accordance with ASU 2015-17. We adopted these provisions prospectively on December 31, 2015, and prior periods were not retrospectively adjusted. We record net deferred tax assets to the extent we believe these assets will more likely than not be realized. In making such determination, we consider all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax planning strategies, recent financial operations and their associated valuation allowances, if any. In the event we were to determine that we would be able to realize or not realize our deferred income tax assets in the future in their net recorded amount, we would make an adjustment to the valuation allowance, which would reduce or increase the provision for income taxes, respectively. Certain provisions of ASC 740, “Income Taxes ” provide that a tax benefit from an uncertain tax position may be recognized when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on the technical merits. I

Earnings per Share

Earnings per Share	12 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Earnings Per Share	Earnings per Share Restricted stock awards we grant to non-employee directors are considered participating securities as they receive non-forfeitable rights to dividends at the same rate as our Common Stock. As participating securities, we include these instruments in the earnings allocation in computing earnings per share under the two-class method described in ASC 260 “ Earnings per Share. ” The following table sets forth the computation of basic and diluted earnings per share under the two-class method (in millions, except per share data): September 30, 2017 2016 2015 Basic earnings (loss) per share: Numerator: Income from continuing operations $ 698.6 $ 154.8 $ 501.2 Less: Net loss (income) from continuing operations attributable to noncontrolling interest 9.6 (2.1 ) (3.3 ) Income available to common stockholders, before discontinued operations 708.2 152.7 497.9 Less: Distributed and undistributed income available to participating securities (0.1 ) — — Distributed and undistributed income attributable to common stockholders, before discontinued operations 708.1 152.7 497.9 (Loss) income from discontinued operations (1) — (549.0 ) 9.2 Net income (loss) attributable to common stockholders $ 708.1 $ (396.3 ) $ 507.1 Denominator: Basic weighted average shares outstanding 252.2 254.0 170.6 Basic earnings per share from continuing operations $ 2.81 $ 0.60 $ 2.92 Basic (loss) earnings per share from discontinued operations — (2.16 ) 0.05 Basic earnings (loss) per share attributable to common stockholders $ 2.81 $ (1.56 ) $ 2.97 Diluted earnings (loss) per share : Numerator: Income from continuing operations $ 698.6 $ 154.8 $ 501.2 Less: Net loss (income) from continuing operations attributable to noncontrolling interest 9.6 (2.1 ) (3.3 ) Income available to common stockholders, before discontinued operations 708.2 152.7 497.9 Less: Distributed and undistributed income available to participating securities (0.1 ) — — Distributed and undistributed income attributable to common stockholders, before discontinued operations 708.1 152.7 497.9 (Loss) Income from discontinued operations (1) — (549.0 ) 9.2 Net income (loss) attributable to common stockholders $ 708.1 $ (396.3 ) $ 507.1 Denominator: Basic weighted average shares outstanding 252.2 254.0 170.6 Effect of dilutive stock options and non-participating securities 3.5 3.9 2.7 Diluted weighted average shares outstanding 255.7 257.9 173.3 Diluted earnings per share from continuing operations $ 2.77 $ 0.59 $ 2.87 Diluted (loss) earnings per share from discontinued operations — (2.13 ) 0.06 Diluted earnings (loss) per share attributable to common stockholders $ 2.77 $ (1.54 ) $ 2.93 (1) Net of income attributable to noncontrolling interests of discontinued operations of $4.3 million and $1.4 million for the fiscal years ended September 30, 2016 and 2015. Weighted average shares include 0.2 million and 0.3 million of reserved, but unissued shares at September 30, 2017 and 2016 . These reserved shares will be distributed as claims are liquidated or resolved in accordance with the resolution of Smurfit-Stone bankruptcy claims. Options and restricted stock in the amount of 0.7 million , 1.6 million and 0.4 million common shares in fiscal 2017 , 2016 and 2015 , respectively, were not included in computing diluted earnings per share because the effect would have been antidilutive. The dilutive impact of the remaining awards outstanding in each year were included in the effect of dilutive securities.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	12 Months Ended
	Sep. 30, 2017
Other Comprehensive Income (Loss) [Abstract]
Comprehensive Income (Loss) Note	Accumulated Other Comprehensive Loss and Other Comprehensive Income (Loss) The following table summarizes the changes in accumulated other comprehensive loss by component for the fiscal years ended September 30, 2017 and 2016 (in millions): Deferred Loss on Cash Flow Hedges Defined Benefit Pension and Postretirement Plans Foreign Currency Items Available for Sale Security Total (1) Balance at September 30, 2015 $ (1.4 ) $ (540.7 ) $ (238.1 ) $ — $ (780.2 ) Other comprehensive (loss) income before reclassifications (0.4 ) (222.2 ) 109.9 — (112.7 ) Amounts reclassified from accumulated other comprehensive loss (2) 1.2 237.2 20.2 — 258.6 Net current period other comprehensive income 0.8 15.0 130.1 — 145.9 Separation of Specialty Chemicals business 0.4 1.9 5.6 — 7.9 Balance at September 30, 2016 $ (0.2 ) $ (523.8 ) $ (102.4 ) $ — $ (626.4 ) Other comprehensive income before reclassifications — 22.8 80.8 0.7 104.3 Amounts reclassified from accumulated other comprehensive (income) loss (0.5 ) 35.6 — — 35.1 Sale of HH&B — 2.9 26.8 — 29.7 Net current period other comprehensive (loss) income (0.5 ) 61.3 107.6 0.7 169.1 Balance at September 30, 2017 $ (0.7 ) $ (462.5 ) $ 5.2 $ 0.7 $ (457.3 ) (1) All amounts are net of tax and noncontrolling interest. (2) Amounts reclasssified from accumulated other comprehensive loss for defined benefit pension and postretirement plans in fiscal 2016 includes the pension risk transfer expense, net of tax. The following table summarizes the reclassifications out of accumulated other comprehensive loss by component for the fiscal years ended September 30, 2017 and 2016 (in millions): Years Ended September 30, 2017 2016 Pretax Tax Net of Tax Pretax Tax Net of Tax Amortization of defined benefit pension and postretirement items: (1) Actuarial losses (2)(3) $ (56.3 ) $ 20.4 $ (35.9 ) $ (379.4 ) $ 143.2 $ (236.2 ) Prior service credits (costs) (2) 0.5 (0.2 ) 0.3 (1.7 ) 0.7 (1.0 ) Sale of HH&B (4) (4.2 ) 1.3 (2.9 ) — — — Subtotal defined benefit plans (60.0 ) 21.5 (38.5 ) (381.1 ) 143.9 (237.2 ) Foreign currency translation adjustments: (1) Sale of HH&B (4) (26.8 ) — (26.8 ) — — — Sale of foreign subsidiary (5) — — — (20.2 ) — (20.2 ) Subtotal foreign currency translation adjustment (26.8 ) — (26.8 ) (20.2 ) — (20.2 ) Derivative Instruments: (1) Commodity currency cash flow hedges (6) — — — (1.5 ) 0.5 (1.0 ) Foreign currency cash flow hedges (7) 0.8 (0.3 ) 0.5 (0.4 ) 0.2 (0.2 ) Subtotal derivative instruments 0.8 (0.3 ) 0.5 (1.9 ) 0.7 (1.2 ) Total reclassifications for the period $ (86.0 ) $ 21.2 $ (64.8 ) $ (403.2 ) $ 144.6 $ (258.6 ) (1) Amounts in parentheses indicate charges to earnings. Amounts pertaining to noncontrolling interests are excluded. (2) These accumulated other comprehensive income components are included in the computation of net periodic pension cost. See “ Note 15. Retirement Plans ” for additional details. (3) Fiscal 2016 includes pension risk transfer expense. (4) Included in gain on sale of HH&B. (5) These accumulated other comprehensive income components are included in interest income and other income (expense), net. (6) These accumulated other comprehensive income components are included in cost of goods sold. (7) These accumulated other comprehensive income components are included in net sales. A summary of the components of other comprehensive income (loss), including noncontrolling interest, for the years ended September 30, 2017 , 2016 and 2015 , is as follows (in millions): Fiscal 2017 Pre-Tax Amount Tax Net of Tax Amount Foreign currency translation gain $ 80.7 $ — $ 80.7 Sale of HH&B, foreign currency 26.8 — 26.8 Reclassification adjustment of net gain on cash flow hedges included in earnings (0.8 ) 0.3 (0.5 ) Net actuarial gain arising during period 34.1 (11.9 ) 22.2 Amortization and settlement recognition of net actuarial loss 56.4 (20.4 ) 36.0 Prior service credit arising during the period 1.0 (0.3 ) 0.7 Amortization of prior service credit (0.4 ) 0.2 (0.2 ) Unrealized gain on available for sale security 0.7 — 0.7 Sale of HH&B, defined benefit pension plans 4.2 (1.3 ) 2.9 Consolidated other comprehensive income 202.7 (33.4 ) 169.3 Less: Other comprehensive income attributable to noncontrolling interests (0.2 ) — (0.2 ) Other comprehensive income attributable to common stockholders $ 202.5 $ (33.4 ) $ 169.1 Fiscal 2016 Pre-Tax Amount Tax Net of Tax Amount Foreign currency translation gain $ 109.8 $ — $ 109.8 Deferred loss on cash flow hedges (0.7 ) 0.3 (0.4 ) Reclassification adjustment of net loss on cash flow hedges included in earnings 1.9 (0.7 ) 1.2 Net actuarial loss arising during period (354.0 ) 129.4 (224.6 ) Amortization and settlement recognition of net actuarial loss (1) 379.7 (143.2 ) 236.5 Prior service credit arising during the period 2.3 (0.9 ) 1.4 Amortization of prior service cost 1.8 (0.7 ) 1.1 Sale of foreign subsidiary 20.2 — 20.2 Consolidated other comprehensive income 161.0 (15.8 ) 145.2 Less: Other comprehensive loss attributable to noncontrolling interests 0.7 — 0.7 Other comprehensive income attributable to common stockholders $ 161.7 $ (15.8 ) $ 145.9 Fiscal 2015 Pre-Tax Amount Tax Net of Tax Amount Foreign currency translation loss $ (242.0 ) $ — $ (242.0 ) Deferred loss on cash flow hedges (2.6 ) 1.0 (1.6 ) Reclassification adjustment of net loss on cash flow hedges included in earnings 0.7 (0.3 ) 0.4 Net actuarial loss arising during period (81.5 ) 28.9 (52.6 ) Amortization and settlement recognition of net actuarial loss 48.1 (17.8 ) 30.3 Prior service cost arising during period (25.0 ) 9.6 (15.4 ) Amortization of prior service credit (7.5 ) 2.9 (4.6 ) Consolidated other comprehensive loss (309.8 ) 24.3 (285.5 ) Less: Other comprehensive loss attributable to noncontrolling interests 0.6 — 0.6 Other comprehensive loss attributable to common stockholders $ (309.2 ) $ 24.3 $ (284.9 ) (1) Includes pension risk transfer expense.

Inventories

Inventories	12 Months Ended
	Sep. 30, 2017
Inventories [Abstract]
Inventories	Inventories Inventories are as follows (in millions): September 30, 2017 2016 Finished goods and work in process $ 905.0 $ 800.6 Raw materials 614.2 535.7 Supplies and spare parts 360.7 335.7 Inventories at FIFO cost 1,879.9 1,672.0 LIFO reserve (82.6 ) (33.8 ) Net inventories $ 1,797.3 $ 1,638.2 It is impracticable to segregate the LIFO reserve between raw materials, finished goods and work in process. In fiscal 2017, we had no LIFO layer liquidations. In fiscal 2016 and 2015, we reduced inventory quantities in some of our LIFO pools. These reductions result in liquidations of LIFO inventory quantities generally carried at lower costs prevailing in prior years as compared with the cost of the purchases in the respective fiscal years, the effect of which typically decreases cost of goods sold. The impact of the liquidations in fiscal 2016 and 2015 was not significant.

Property, Plant and Equipment (

Property, Plant and Equipment (Notes)	12 Months Ended
	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment Disclosure [Text Block]	Property, Plant and Equipment Property, plant and equipment consists of the following (in millions): September 30, 2017 2016 Property, plant and equipment at cost: Land and buildings $ 2,034.3 $ 2,307.9 Machinery and equipment 11,349.7 10,672.9 Forestlands and mineral rights 208.3 201.1 Transportation equipment 30.7 27.6 Leasehold improvements 59.5 62.4 13,682.5 13,271.9 Less: accumulated depreciation and amortization (4,564.2 ) (3,977.6 ) Property, plant and equipment, net $ 9,118.3 $ 9,294.3 Depreciation expense, excluding discontinued operations, for fiscal 2017 , 2016 and 2015 was $855.9 million , $848.9 million and $578.4 million , respectively. See “ Note 7. Discontinued Operations ” for additional information.

Acquisitions

Acquisitions	12 Months Ended
	Sep. 30, 2017
Acquisitions [Abstract]
Acquisitions	Merger, Acquisitions and Investment Hannapak Acquisition On August 1, 2017, we completed the Hannapak Acquisition in a stock purchase. Hanna Group is one of Australia’s leading providers of folding cartons to a variety of markets, including beverage, food, confectionery, and healthcare. We expect this acquisition will build on our established and growing packaging business in the region. The purchase consideration for the Hannapak Acquisition was $59.4 million , net of cash received of $0.6 million and an unreceived working capital settlement of $2.4 million . We have included the financial results of the acquired assets since the date of the acquisition in our Consumer Packaging segment. The preliminary allocation of consideration primarily included $14.5 million of customer relationship intangible assets, $20.1 million of goodwill, $13.9 million of property, plant and equipment and $7.1 million of liabilities. We are amortizing the customer relationship intangibles over 13 years based on a straight-line basis because the amortization pattern was not reliably determinable. The fair value assigned to goodwill is primarily attributable to buyer-specific synergies expected to arise after the acquisition (e.g., enhanced reach of the combined organization and other synergies), and the assembled work force. The goodwill and intangibles are not amortizable for income tax purposes. We are in the process of reviewing the estimated fair values of all assets acquired and liabilities assumed, including, among other things, obtaining final valuations of certain tangible and intangible assets as well as the fair value of certain contracts and the determination of certain tax balances; thus, the allocation of the purchase price is preliminary and subject to revision. Island Container Acquisition On July 17, 2017, we completed the Island Container Acquisition in an asset purchase. The assets acquired include a corrugator and corrugated converting operations located in Wheatley Heights, New York, and certain related fulfillment assets located in Saddle Brook, New Jersey. We expect this acquisition will enable us to integrate more than 80,000 tons of containerboard annually into our Corrugated Packaging segment. The purchase consideration for the Island Container Acquisition was $84.7 million , including an estimated unpaid working capital settlement of $1.2 million . We have included the financial results of the acquired assets since the date of the acquisition in our Corrugated Packaging segment. The preliminary allocation of consideration primarily included $43.0 million of customer relationship intangible assets, $27.2 million of goodwill, $5.4 million of property, plant and equipment and $1.2 million of liabilities. We are amortizing the customer relationship intangibles over 8.5 years based on a straight-line basis because the amortization pattern was not reliably determinable. The fair value assigned to goodwill is primarily attributable to buyer-specific synergies expected to arise after the acquisition (e.g., enhanced reach of the combined organization and other synergies), and the assembled work force. The goodwill and intangibles are amortizable for income tax purposes. We are in the process of reviewing the estimated fair values of all assets acquired and liabilities assumed, including, among other things, obtaining final third-party valuations of certain tangible and intangible assets as well as the fair value of certain contracts and the determination of certain tax balances; thus, the allocation of the purchase price is preliminary and subject to revision. MPS Acquisition On June 6, 2017, we completed the MPS Acquisition in a stock purchase. MPS is a global provider of print-based specialty packaging solutions and its differentiated product offering includes premium folding cartons, inserts, labels and rigid packaging. We acquired the outstanding shares of MPS for $18.00 per share in cash and the assumption of debt. We believe this acquisition increases annual paperboard consumption by approximately 225,000 tons, of which we expect 35% to 45% to be supplied by us. In connection with the MPS Acquisition, we paid cash of $1,351.1 million , net of cash received of $47.5 million . The purchase consideration included the assumption of $929.1 million of debt and $1.9 million related to MPS equity awards that were replaced with WestRock equity awards with identical terms for the pre-acquisition service. The amount related to post-acquisition service is being expensed over the remaining service period of the awards. See “ Note 17. Share-Based Compensation ” for additional information on the converted awards. We have included the financial results of MPS since the date of the acquisition in our Consumer Packaging segment. The preliminary allocation of consideration primarily included $1,017.6 million of intangible assets, $887.7 million of goodwill, $486.3 million of property, plant and equipment and $1,554.7 million of liabilities and noncontrolling interests, including debt and deferred income taxes. The fair value assigned to goodwill is primarily attributable to buyer-specific synergies expected to arise after the acquisition (e.g., enhanced reach of the combined organization and other synergies), the assembled work force, as well as due to establishing deferred taxes for the difference between book and tax basis of the assets and liabilities acquired. The goodwill and intangibles are not amortizable for income tax purposes. We are in the process of reviewing the estimated fair values of all assets acquired and liabilities assumed, including, among other things, obtaining final third-party valuations of certain tangible and intangible assets as well as the fair value of certain contracts and the determination of certain tax balances; thus, the allocation of the purchase price is preliminary and subject to revision. The following table summarizes the weighted average life and the preliminary allocation to intangible assets recognized in the MPS Acquisition, excluding goodwill (in millions): Weighted Avg. Life Amounts Recognized as of the Acquisition Date Customer relationships 14.6 $ 999.9 Trademarks and tradenames 3.0 15.2 Photo library 10.0 2.5 Total 14.4 $ 1,017.6 None of the intangibles has significant residual value. We are amortizing the customer relationship intangibles over estimated useful lives ranging from 13 to 16 years based on a straight-line basis because the amortization pattern was not reliably determinable. U.S. Corrugated Acquisition On June 9, 2017, we completed the U.S. Corrugated Acquisition in a stock purchase. We acquired five corrugated converting facilities in Ohio, Pennsylvania and Louisiana that provide a comprehensive suite of products and services to customers in a variety of end markets, including food & beverage, pharmaceuticals and consumer electronics. We believe the acquisition will enable us to increase the vertical integration of our Corrugated Packaging segment by approximately 105,000 tons of containerboard annually through the acquired facilities and another 50,000 tons under a long-term supply contract with another company owned by the seller. The purchase consideration was $193.7 million , net of cash received of $1.4 million and an unreceived working capital settlement of $3.4 million . The consideration included the issuance of 2.4 million shares of Common Stock valued at $136.1 million . We have included the financial results of the acquired assets since the date of the acquisition in our Corrugated Packaging segment. The preliminary allocation of consideration primarily included $77.8 million of customer relationship intangible assets, $108.2 million of goodwill, $30.0 million of property, plant and equipment and $53.2 million of liabilities, including deferred income taxes. We are amortizing the customer relationship intangibles over 7.5 years based on a straight-line basis because the amortization pattern was not reliably determinable. The fair value assigned to goodwill is primarily attributable to buyer-specific synergies expected to arise after the acquisition (e.g., enhanced reach of the combined organization and other synergies), and the assembled work force, as well as due to establishing deferred taxes for the difference between book and tax basis of the assets and liabilities acquired. The goodwill and intangibles are not amortizable for income tax purposes. We are in the process of reviewing the estimated fair values of all assets acquired and liabilities assumed, including, among other things, obtaining final third-party valuations of certain tangible and intangible assets as well as the fair value of certain contracts and the determination of certain tax balances; thus, the allocation of the purchase price is preliminary and subject to revision. Star Pizza Acquisition On March 13, 2017, we completed the Star Pizza Acquisition. The transaction provides us with a leadership position in the fast growing small-run pizza box market and increases our vertical integration. The purchase price was $34.6 million , net of a $0.7 million working capital settlement. We have included the financial results of the acquired assets since the date of the acquisition in our Corrugated Packaging segment. The preliminary purchase price allocation for the acquisition primarily included $24.8 million of customer relationship intangible assets and $2.2 million of goodwill. We are amortizing the customer relationship intangibles over 10 years based on a straight-line basis because the amortization pattern was not reliably determinable. The fair value assigned to goodwill is primarily attributable to buyer-specific synergies expected to arise after the acquisition (e.g., enhanced reach of the combined organization and other synergies), and the assembled work force. We expect the goodwill and intangibles to be amortizable for income tax purposes. We are in the process of reviewing the estimated fair values of all assets acquired and liabilities assumed; thus, the allocation of the purchase price is preliminary and subject to revision. Grupo Gondi Investment On April 1, 2016, we completed the formation of a joint venture with Grupo Gondi in Mexico. We contributed $175.0 million in cash and the stock of an entity that owns three corrugated packaging facilities in Mexico in return for a 25.0 % equity participation in the joint venture together with future put and call rights. The investment was valued at approximately $0.3 billion . The joint venture operates paper machines, corrugated packaging and high graphic folding carton facilities across various production sites. The majority equity holders manage the joint venture and we provide technical and commercial resources and supply certain paperboard to the joint venture. We believe the joint venture will help grow our presence in the attractive Mexican market. As a result of the transaction, we recorded a pre-tax non-cash gain of $12.1 million included in “Interest income and other income (expense), net” on our Consolidated Statements of Operations in fiscal 2016. The transaction includes future put and call rights with respect to the respective parties’ ownership interest in the joint venture. We have included the financial results of the joint venture since the date of the formation in our Corrugated Packaging segment, and are accounting for the investment under the equity method. In the third quarter of fiscal 2017, the joint venture entity had a stock redemption from a minority partner. As a result, our equity participation in the joint venture increased to approximately 27.0% . The transaction continues to include future put and call rights with respect to the respective parties’ ownership interest in the joint venture. See “ Note 23. Subsequent Events (Unaudited) — Grupo Gondi Investment ” for recent developments. Packaging Acquisition On January 19, 2016, we completed the Packaging Acquisition. The entities acquired provide value-added folding carton and litho-laminated display packaging solutions. The purchase price was $94.1 million , net of cash received of $1.7 million , a working capital settlement and a $3.5 million escrow receipt in the first quarter of fiscal 2017. The transaction is subject to an election under Section 338(h)(10) of the Code that increases the U.S. tax basis in the acquired U.S. entities. We believe the transaction has provided us with attractive and complementary customers, markets and facilities. We have included the financial results of the acquired entities since the date of the acquisition in our Consumer Packaging segment. The purchase price allocation for the acquisition primarily included $55.0 million of property, plant and equipment, $10.5 million of customer relationship intangible assets, $9.3 million of goodwill and $25.8 million of liabilities, including $1.3 million of debt. We are amortizing the customer relationship intangibles over estimated useful lives ranging from 9 to 15 years based on a straight-line basis because the amortization pattern was not reliably determinable. The fair value assigned to goodwill is primarily attributable to buyer-specific synergies expected to arise after the acquisition (e.g., enhanced reach of the combined organization and other synergies), and the assembled work force. The goodwill and intangibles of the U.S. entities are amortizable for income tax purposes. SP Fiber On October 1, 2015, completed the SP Fiber Acquisition in a stock purchase. The transaction included the acquisition of mills located in Dublin, GA and Newberg, OR, which produce lightweight recycled containerboard and kraft and bag paper. The Newberg mill also produced newsprint. As part of the transaction, we also acquired SP Fiber's 48 % interest in GPS. GPS is a joint venture providing steam to the Dublin mill and electricity to Georgia Power. The purchase price was $278.8 million , net of cash received of $9.2 million and a working capital settlement. In addition, we paid $36.5 million for debt owed by GPS and thereby own the majority of the debt issued by GPS. The Dublin mill has helped balance the fiber mix of our mill system, including our ability to serve the increasing demand for lighter weight containerboard, and the addition of kraft and bag paper has diversified our product offering. Subsequent to the transaction, we announced the permanent closure of the Newberg mill due to the decline in market conditions of the newsprint business and our need to balance supply and demand in our containerboard system. We determined GPS should be consolidated as a variable interest entity under ASC 810 “ Consolidation ”. Our evaluation concluded that WestRock is the primary beneficiary of GPS as WestRock has both the power and benefits as defined by ASC 810. We have included the financial results of SP Fiber and GPS since the date of the acquisition in our Corrugated Packaging segment. The purchase price allocation for the acquisition primarily included $324.8 million of property, plant and equipment, $13.5 million of customer relationship intangible assets, $57.3 million of goodwill, and $150.3 million of liabilities and noncontrolling interests, including $13.7 million of debt primarily owed by GPS to third parties. We are amortizing the customer relationship intangibles over 20 years based on a straight-line basis because the amortization pattern was not reliably determinable. The fair value assigned to goodwill is primarily attributable to buyer-specific synergies expected to arise after the acquisition (e.g., enhanced reach of the combined organization and other synergies), the assembled work force of SP Fiber as well as due to establishing deferred taxes for the difference between the book to tax basis of the assets and liabilities acquired. The goodwill and intangibles are not amortizable for income tax purposes. The Combination On July 1, 2015, pursuant to the Business Combination Agreement, RockTenn and MWV completed a strategic combination of their respective businesses. Pursuant to the Business Combination Agreement, RockTenn and MWV each became wholly-owned subsidiaries of WestRock. RockTenn was the accounting acquirer. We believe the Combination combined two industry leaders to create a leading global provider of consumer and corrugated packaging solutions. The consideration for the Combination was $8,286.7 million . In connection with the Combination, RockTenn shareholders received in the aggregate approximately 130.4 million shares of Common Stock and approximately $667.8 million in cash. At the effective time of the Combination, each share of common stock, par value $0.01 per share, of MWV issued and outstanding immediately prior to the effective time of the Combination was converted into the right to receive 0.78 shares of Common Stock. In the aggregate, MWV stockholders received approximately 131.2 million shares of our Common Stock (which includes shares issued under certain MWV equity awards that vested as a result of the Combination). Included in the consideration was approximately $210.9 million related to outstanding MWV equity awards that were replaced with WestRock equity awards with identical terms for pre-Combination service. The amount related to post-Combination service is being expensed over the remaining service period of the awards. The following table summarizes the fair values of the assets acquired and liabilities assumed by major class of assets and liabilities as of the acquisition date, as well as adjustments made during fiscal 2016 (referred to as “measurement period adjustments”) (in millions): Amounts Recognized as of the Acquisition Date Measurement Period Adjustments (1) Amounts Recognized as of Acquisition Date (as Adjusted) (2) Cash and cash equivalents $ 265.7 $ — $ 265.7 Current assets, excluding cash and cash equivalents 1,858.8 (0.5 ) 1,858.3 Property, plant and equipment 3,991.5 19.3 4,010.8 Prepaid pension asset 1,407.8 (9.9 ) 1,397.9 Goodwill 3,817.3 44.7 3,862.0 Intangible assets 2,994.2 — 2,994.2 Restricted assets held by special purpose entities 1,302.0 — 1,302.0 Other long-term assets 363.8 18.0 381.8 Total assets acquired 16,001.1 71.6 16,072.7 Current portion of debt 62.3 74.8 137.1 Current liabilities 1,099.4 (45.6 ) 1,053.8 Long-term debt due after one year 2,090.6 18.3 2,108.9 Non-recourse liabilities held by special purpose entities 1,181.0 — 1,181.0 Accrued pension and other long-term benefits 235.1 — 235.1 Deferred income tax liabilities 2,366.7 (11.0 ) 2,355.7 Other long-term liabilities 520.0 35.1 555.1 Noncontrolling interest 159.3 — 159.3 Total liabilities and noncontrolling interest assumed 7,714.4 71.6 7,786.0 Net assets acquired (3) $ 8,286.7 $ — $ 8,286.7 (1) The measurement period adjustments recorded in fiscal 2016 did not have a significant impact on our consolidated statements of operations for fiscal 2016 or 2015. In addition, these adjustments did not have a significant impact on our consolidated balance sheet as of September 30, 2015. Therefore, we have recorded the cumulative impact in fiscal 2016 and have not retrospectively adjusted the comparative 2015 financial information presented herein. (2) The measurement period adjustments were due primarily to refinements to third party appraisals and carrying amounts of certain assets and liabilities as well as adjustments to certain tax accounts based on, among other things, adjustments to deferred tax liabilities, including any appraisal adjustments, analysis of the tax basis of acquired assets and liabilities, other tax adjustments and the classification of supplier financing arrangements. The net impact of the measurement period adjustments resulted in a net increase to goodwill. (3) The net assets acquired include the Specialty Chemicals business, which was separated from WestRock on May 15, 2016 . See “ Note 7. Discontinued Operations ” for additional information. The fair value assigned to goodwill is primarily attributable to buyer-specific synergies expected to arise after the acquisition (e.g., enhanced geographic reach of the combined organization, increased vertical integration and other synergistic opportunities), the assembled work force of MWV as well as due to establishing deferred tax liabilities for the assets and liabilities acquired. The goodwill and intangibles resulting from the acquisition will not be amortizable for tax purposes. See “ Note 21. Segment Information ” for the allocation of goodwill. The following table summarizes the weighted average life and gross carrying amount relating to intangible assets recognized in the Combination, excluding goodwill (in millions): Weighted Avg. Life Gross Carrying Amount Customer relationships 19.2 $ 2,881.7 Patents 9.8 57.2 Trademarks and tradenames 4.5 52.9 Favorable contracts 8.2 2.4 Total 18.8 $ 2,994.2 None of the intangibles has significant residual value. The intangibles are expected to be amortized over estimated useful lives ranging from 1 to 20 years based on the approximate pattern in which the economic benefits are consumed or straight-line if the pattern was not reliably determinable. The allocation of the consideration for the Combination also includes, among other things, $38.5 million of liabilities for unfavorable contracts which will be amortized over 1 to 9 years. In connection with purchase accounting, we increased the carrying value of the debt assumed by $364.5 million , including $18.3 million in the third quarter of fiscal 2016 to increase the carrying value of the debt assumed to fair value. The fair value adjustment will be amortized over the life of the instruments, ranging from 1 to 32 years. The following unaudited pro forma information reflects our consolidated results of operations as if the Combination had taken place on October 1, 2013. The unaudited pro forma information is not necessarily indicative of the results of operations that we would have reported had the transaction actually occurred at the beginning of these periods nor is it necessarily indicative of future results. The unaudited pro forma financial information does not reflect the impact of future events that may occur after the Combination, including, but not limited to, anticipated costs savings from synergies or other operational improvements. The net sales have been adjusted to reflect the discontinued operations of the Specialty Chemicals business. Year Ended September 30, 2015 (Unaudited, in millions) Net sales $ 14,347.0 Net income attributable to common stockholders $ 666.3 Fiscal 2015 revenues associated with the MWV operations received in the Combination since the closing date were $1,067.1 million . Disclosure of earnings associated with these operations since the closing date for fiscal 2015 is not practicable as it is not being operated as a standalone business. The unaudited pro forma financial information presented in the table above has been adjusted to give effect to adjustments that are (1) directly related to the business combination; (2) factually supportable; and (3) expected to have a continuing impact. These adjustments include, but are not limited to, the application of our accounting policies; elimination of related party transactions; depreciation and amortization related to fair value adjustments to property, plant and equipment and intangible assets including contracts assumed; and interest expense on acquisition related debt. Unaudited pro forma earnings for fiscal 2015 were adjusted to exclude $126.7 million of acquisition related costs which primarily consist of advisory, legal, accounting, valuation, other professional or consulting fees and change in control related acceleration of share-based compensation, $71.6 million for the expensing of inventory stepped-up in purchase accounting, net of related LIFO impact and $2.6 million of loss on extinguishment of debt. Included in earnings for fiscal 2015 are $75.5 million of integration related costs related to the Combination which primarily consist of severance and other employee costs and professional services. In fiscal 2017, we recategorized our integration costs to exclude severance and other employee costs. These costs have now been presented as restructuring costs. We recategorized $48.2 million related to fiscal 2015. See “ Note 9. Restructuring and Other Costs, Net ”.

Discontinued Operations (Notes)

Discontinued Operations (Notes)	12 Months Ended
	Sep. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Groups, Including Discontinued Operations, Disclosure [Text Block]	Discontinued Operations On May 15, 2016 , WestRock completed the Separation. We distributed 100% of the outstanding common stock, par value $0.01 per share, of Ingevity, then a wholly-owned subsidiary of WestRock, to WestRock’s stockholders of record as of the close of business on May 4, 2016 , with such stockholders receiving one share of Ingevity common stock for every six shares of Common Stock held as of such record date. Since the Separation, we have not beneficially owned any shares of Ingevity common stock and Ingevity has been an independent public company trading under the symbol “NGVT” on the NYSE. We disposed of the former Specialty Chemicals segment in its entirety and ceased to consolidate its assets, liabilities and results of operations. Accordingly, we have presented the financial position and results of operations of our former Specialty Chemicals segment as discontinued operations in the accompanying consolidated financial statements for all periods presented. In connection with the Separation, we and Ingevity entered into a separation and distribution agreement as well as various other agreements that provide a framework for the relationships between the parties going forward, including among others a tax matters agreement, a lease and ground service agreement with respect to our Covington, Virginia facility, an intellectual property agreement, a crude tall oil and black liquor soap skimming supply agreement, a trust agreement, an employee matters agreement and a transition service agreement. These agreements provided for the allocation between us and Ingevity of assets, employees, liabilities and obligations attributable to periods prior to, at and after the Separation and govern certain relationships between us and Ingevity after the Separation. Prior to the Separation, Ingevity, then a wholly-owned subsidiary of WestRock, borrowed $500.0 million in contemplation of the Separation and distributed the majority of these funds to WestRock, which used the funds to pay down debt. In addition, Ingevity assumed an $80.0 million , 7.67% capital lease obligation due January 15, 2027 owed to the City of Wickliffe, KY. In contemplation of the Separation, Ingevity also funded a trust in the amount of $68.9 million to secure the balloon principal payment of the capital lease upon the lease’s maturity. We remain a co-obligor on the capital lease obligation; therefore, the capital lease assumed by Ingevity remains recorded in our consolidated financial statements in long-term debt. At the time of the Separation, we recorded a $108.2 million long-term asset for the estimated fair value of the future principal and interest payments on the capital lease obligation assumed by Ingevity. The value of the long-term asset and the long-term debt under the lease will reduce over the life of the lease using the effective interest method. The $500.0 million of debt and the $68.9 million in the trust were assumed by Ingevity, and removed from our consolidated financial statements as part of our discontinued operations reporting. The following table presents the financial results of Specialty Chemicals’ discontinued operations (in millions): Fiscal Year Ended September 30, 2016 2015 Net sales $ 533.7 $ 256.5 Cost of goods sold 387.5 184.0 Gross profit 146.2 72.5 Selling, general and administrative, excluding intangible amortization 65.6 27.4 Selling, general and administrative intangible amortization 28.8 11.5 Restructuring and other costs, net 49.5 6.6 Impairment of Specialty Chemicals goodwill and intangibles 579.4 — Operating (loss) profit (577.1 ) 27.0 Interest income (expense) and other income (expense), net 0.1 1.1 (Loss) income from discontinued operations before income taxes (577.0 ) 28.1 Income tax benefit (expense) 32.3 (17.5 ) (Loss) income from discontinued operations $ (544.7 ) $ 10.6 Fiscal 2016 restructuring and other costs, net are primarily associated with costs incurred to support the Separation and consist primarily of advisory, legal, accounting and other professional fees. Additionally, restructuring and other costs, net include $10.0 million of costs associated with the closure of Ingevity’s Duque de Caxias facility in Brazil and other severance and share-based compensation expenses. Fiscal 2015 restructuring and other costs, net are primarily associated with costs incurred to support the Separation and consist primarily of advisory, legal, accounting and other professional fees. In the first quarter of fiscal 2016, as part of our evaluation of whether events or changes in circumstances had occurred that would indicate whether it was more likely than not that the goodwill of our then-owned Specialty Chemicals reporting unit was impaired, we considered factors such as, but not limited to, macroeconomic conditions, industry and market considerations, and financial performance, including the planned revenue and earnings of the reporting unit. We concluded that an impairment indicator had occurred related to the goodwill of the Specialty Chemicals reporting unit and that the indicator was driven by market factors subsequent to the Combination. Accordingly, we performed a “Step 1” goodwill impairment test where we updated the discounted cash flow analysis used to determine the reporting unit’s initial fair value on July 1, 2015. We also compared those results to the valuations performed by our investment bankers in connection with the planned separation of our Specialty Chemicals business. Based on the results of the impairment test and analysis, we concluded that the fair value of the Specialty Chemicals reporting unit was less than its carrying amount and began a “Step 2” goodwill impairment test to determine the amount of impairment loss, if any. As part of the analysis, we determined that the carrying value of the property, plant and equipment and intangibles, all of which have finite lives, on a “held and used” basis did not exceed the estimated undiscounted future cash flows. In light of changing market conditions, expected revenue and earnings of the reporting unit, lower comparative market valuations for companies in Specialty Chemicals’ peer group and our preliminary “Step 2” test, we concluded that an impairment of the Specialty Chemicals reporting unit was probable and could be reasonably estimated. As a result, we recorded a pre-tax and after-tax non-cash goodwill impairment charge of $478.3 million . This amount is included in the line item “Loss from discontinued operations” in the Consolidated Statements of Operations. No tax benefit was recorded for the goodwill impairment. Until the completion of the Separation, GAAP required us to assess impairment of the Specialty Chemicals’ long-lived assets using the “held and used” model which was based on undiscounted future cash flows. Under this model, if the expected cash flows over the life of the primary asset of the reporting unit were in excess of the carrying amount, then there would be no impairment. At the date of the Separation, we assessed Specialty Chemical’s assets for potential impairment using the “held for sale” model. This model compares the fair value of the disposal unit to its carrying value and if the fair value less cost to sell is lower, then an impairment loss would be recorded. At the date of the Separation, we evaluated the Specialty Chemical’s intangibles, which consisted predominantly of customer list intangibles, for impairment. Our analysis at May 15, 2016 , using the income approach (multi-period excess earnings method), indicated that there was a $101.1 million pre-tax non-cash impairment of our Specialty Chemicals customer relationships intangible. The impairment loss was recorded on the Separation and is included as a component of discontinued operations. The following table presents the significant non-cash items and capital expenditures for Specialty Chemicals’ that are included in the Consolidated Statements of Cash Flows (in millions): Fiscal Year Ended September 30, 2016 2015 Depreciation, depletion and amortization $ 57.2 $ 22.0 Impairment of Specialty Chemicals goodwill and intangibles $ 579.4 $ — Capital expenditures $ (45.2 ) $ (28.6 ) Depreciation expense in fiscal 2016 and 2015 was $30.4 million and $11.4 million , respectively, and amortization expense in fiscal 2016 and 2015 was $26.8 million and $10.6 million , respectively.

Assets Held For Sale (Notes)

Assets Held For Sale (Notes)	12 Months Ended
	Sep. 30, 2017
Assets Held for Sale [Text Block]	Assets Held For Sale During the second quarter of fiscal 2017, we committed to a plan to sell HH&B. On January 23, 2017, we announced we had entered into an agreement with certain subsidiaries of Silgan under which Silgan would purchase HH&B for approximately $1.025 billion in cash plus the assumption of approximately $25 million in foreign pension liabilities. Accordingly, in the second quarter of fiscal 2017, all of the assets and liabilities of HH&B were reported as assets and liabilities held for sale. We discontinued recording depreciation and amortization while the assets were held for sale. On April 6, 2017, we announced that we had completed the HH&B Sale. We used the proceeds from the HH&B Sale in connection with the MPS Acquisition. We recorded a pre-tax gain on sale of HH&B of $192.8 million in fiscal 2017. Due to the accelerated monetization strategy, our Land and Development portfolio has met the held for sale criteria and is reflected as assets held for sale. Assets held for sale at September 30, 2017 of $173.6 million include $150.4 million of Land and Development portfolio assets, with the remainder primarily related to closed facilities. As of September 30, 2016, the $52.3 million of assets held for sale were primarily related to assets under contract in our Land and Development segment.

Restructuring and Other Costs,

Restructuring and Other Costs, Net	12 Months Ended
	Sep. 30, 2017
Restructuring and Other Costs, Net [Abstract]
Restructuring and Other Costs, Net	Restructuring and Other Costs, Net Summary of Restructuring and Other Initiatives We recorded pre-tax restructuring and other costs, net, of $196.7 million , $366.4 million and $140.8 million for fiscal 2017 , 2016 and 2015 , respectively. Of these costs, $86.6 million , $200.2 million and $13.4 million were non-cash for fiscal 2017 , 2016 and 2015 , respectively. These amounts, which are outlined below, are not comparable since the timing and scope of the individual actions associated with each restructuring, acquisition, divestiture or integration can vary. The restructuring and other costs, net, exclude the Specialty Chemicals costs which are included in discontinued operations. We present our restructuring and other costs, net in more detail below and those charged to discontinued operations in “ Note 7. Discontinued Operations ”. The following table summarizes our Restructuring and other costs, net for fiscal 2017 , 2016 and 2015 (in millions): Fiscal 2017 Fiscal 2016 Fiscal 2015 Restructuring $ 113.4 $ 294.9 $ 60.3 Other 83.3 71.5 80.5 Restructuring and Other Costs, net $ 196.7 $ 366.4 $ 140.8 Restructuring Our restructuring charges are primarily associated with plant closures and employee costs due to merger and acquisition-related workforce reductions. When we close a facility, if necessary, we recognize an impairment charge primarily to reduce the carrying value of equipment or other property to their estimated fair value less cost to sell, and record charges for severance and other employee-related costs. Any subsequent change in fair value less cost to sell prior to disposition is recognized as identified; however, no gain is recognized in excess of the cumulative loss previously recorded. At the time of each announced closure, we generally expect to record future period costs for equipment relocation, facility carrying costs, costs to terminate a lease or contract before the end of its term and employee-related costs. Although specific circumstances vary, our strategy has generally been to consolidate our sales and operations into large well-equipped plants that operate at high utilization rates and take advantage of available capacity created by operational excellence initiatives and/or further optimize our system following mergers and acquisitions or a changing business environment. Therefore, we have transferred a substantial portion of each closed plant’s assets and production to our other plants. We believe these actions have allowed us to more effectively manage our business. In our Land and Development segment, the restructuring charges primarily relate to severance and other employee costs associated with the accelerated monetization strategy and wind down of operations. While restructuring costs are not charged to our segments and, therefore, do not reduce segment income, we highlight the segment to which the charges relate. The following table presents a summary of restructuring charges related to active restructuring initiatives that we incurred during the last three fiscal years, the cumulative recorded amount since we started the initiative, and our estimate of the total we expect to incur (in millions): Fiscal 2017 Fiscal 2016 Fiscal 2015 Cumulative Total Expected Corrugated Packaging Net property, plant and equipment costs $ 1.4 $ 184.5 $ 1.3 $ 221.0 $ 221.0 Severance and other employee costs 3.3 17.4 0.4 43.2 45.1 Equipment and inventory relocation costs 1.9 0.3 1.1 6.5 9.0 Facility carrying costs 5.4 18.9 3.0 36.4 39.7 Other costs (1.2 ) 9.1 2.2 20.5 20.5 Restructuring total $ 10.8 $ 230.2 $ 8.0 $ 327.6 $ 335.3 Consumer Packaging Net property, plant and equipment costs $ 28.3 $ 3.8 $ 0.9 $ 37.5 $ 37.5 Severance and other employee costs 26.4 4.6 1.8 34.4 34.4 Equipment and inventory relocation costs 2.8 1.1 0.5 4.9 7.4 Facility carrying costs 0.7 0.5 0.9 2.4 3.8 Other costs (1) 20.2 — 0.3 20.7 20.7 Restructuring total $ 78.4 $ 10.0 $ 4.4 $ 99.9 $ 103.8 Land and Development Net property, plant and equipment costs $ 1.8 $ — $ — $ 1.8 $ 1.8 Severance and other employee costs 2.8 10.6 — 13.4 14.5 Restructuring total $ 4.6 $ 10.6 $ — $ 15.2 $ 16.3 Corporate Net property, plant and equipment costs $ 0.1 $ 1.2 $ — $ 1.4 $ 1.4 Severance and other employee costs 14.8 36.9 48.2 99.9 99.9 Other costs 4.7 6.0 (0.3 ) 10.4 10.4 Restructuring total $ 19.6 $ 44.1 $ 47.9 $ 111.7 $ 111.7 Total Net property, plant and equipment costs $ 31.6 $ 189.5 $ 2.2 $ 261.7 $ 261.7 Severance and other employee costs 47.3 69.5 50.4 190.9 193.9 Equipment and inventory relocation costs 4.7 1.4 1.6 11.4 16.4 Facility carrying costs 6.1 19.4 3.9 38.8 43.5 Other costs 23.7 15.1 2.2 51.6 51.6 Restructuring total $ 113.4 $ 294.9 $ 60.3 $ 554.4 $ 567.1 (1) Includes a $17.6 million impairment of a customer relationship intangible in fiscal 2017 related to an exited product line. We have defined “ Net property, plant and equipment ” as used in this Note 9 as property, plant and equipment impairment losses, subsequent adjustments to fair value for assets classified as held for sale, subsequent (gains) or losses on sales of property, plant and equipment and related parts and supplies, and accelerated depreciation on such assets, if any. Other Costs Our other costs consist of acquisition, divestiture and integration costs. We incur costs when we acquire or divest businesses. Acquisition costs include costs associated with transactions, whether consummated or not, such as advisory, legal, accounting, valuation and other professional or consulting fees, as well as potential litigation costs associated with those activities. Divestiture costs consist primarily of similar professional fees. The divestiture costs in fiscal 2017 are primarily associated with costs incurred during the HH&B Sale process. Post-acquisition, we incur integration costs that reflect work being performed to facilitate merger and acquisition integration, such as work associated with information systems and other projects, and primarily consist of professional services. We consider acquisition, divestiture and integration costs to be Corporate costs regardless of the segment or segments involved in the transaction. The following table presents our acquisition, divestiture and integration costs that we incurred during the last three fiscal years (in millions): Fiscal 2017 Fiscal 2016 Fiscal 2015 Acquisition costs $ 27.1 $ 8.9 $ 44.4 Divestiture costs 9.8 0.5 — Integration costs 46.4 62.1 36.1 Other total $ 83.3 $ 71.5 $ 80.5 In fiscal 2017, we recategorized our integration costs to exclude severance and other employee costs and lease costs associated with mergers and acquisitions, notably for related workforce reductions. These costs have been presented in severance and other employee costs and other costs, respectively, in the restructuring table above. We recategorized $42.6 million and $48.2 million in fiscal 2016 and 2015, respectively, primarily for severance and other employee costs. We had $17.4 million of similar costs in fiscal 2017. The following table represents a summary of and the changes in the restructuring accrual, which is primarily composed of lease commitments, accrued severance and other employee costs, and a reconciliation of the restructuring accrual charges to the line item “Restructuring and other costs, net” on our Consolidated Statements of Operations for fiscal 2017 , 2016 and 2015 (in millions): 2017 2016 2015 Accrual at beginning of fiscal year $ 44.8 $ 21.4 $ 10.9 Accruals acquired in purchase accounting 3.5 — 2.9 Additional accruals 63.2 75.3 37.6 Payments (53.3 ) (51.9 ) (31.4 ) Adjustment to accruals (10.8 ) — 1.4 Accrual at end of fiscal year $ 47.4 $ 44.8 $ 21.4 Reconciliation of accruals and charges to restructuring and other costs, net (in millions): 2017 2016 2015 Additional accruals and adjustments to accruals (see table above) $ 52.4 $ 75.3 $ 39.0 Acquisition costs 27.1 8.9 44.4 Divestiture costs 9.8 0.5 — Integration costs 41.2 59.8 36.8 Net property, plant and equipment 31.6 189.5 2.2 Severance and other employee costs 3.8 11.5 12.7 Equipment and inventory relocation costs 4.7 1.4 1.6 Facility carrying costs 6.1 19.5 3.9 Other costs 20.0 — 0.2 Total restructuring and other costs, net $ 196.7 $ 366.4 $ 140.8

Other Intangible Assets

Other Intangible Assets	12 Months Ended
	Sep. 30, 2017
Other Intangible Assets [Abstract]
Other Intangible Assets	Other Intangible Assets The gross carrying amount and accumulated amortization relating to intangible assets, excluding goodwill, is as follows (in millions, except weighted avg. life): September 30, 2017 2016 Weighted Avg. Life (in years) Gross Carrying Amount Accumulated Amortization Gross Carrying Amount Accumulated Amortization Customer relationships 16.7 $ 4,046.2 $ (806.0 ) $ 3,094.4 $ (610.5 ) Favorable contracts 9.6 48.2 (30.7 ) 48.9 (27.0 ) Technology and patents 10.7 31.8 (14.4 ) 55.4 (14.9 ) Trademarks and tradenames 16.3 74.7 (31.4 ) 65.0 (24.1 ) Non-compete agreements 2.0 2.5 (0.6 ) 0.2 (0.1 ) License costs 8.8 23.6 (14.6 ) 23.5 (11.5 ) Total 16.6 $ 4,227.0 $ (897.7 ) $ 3,287.4 $ (688.1 ) Intangible amortization expense, excluding discontinued operations, was $256.2 million , $235.8 million and $131.1 million during fiscal 2017 , 2016 and 2015 , respectively. The intangible amortization expense is primarily recorded as SG&A intangible amortization. See “ Note 7. Discontinued Operations ” for additional information. Estimated intangible asset amortization expense for the succeeding five fiscal years is as follows (in millions): Fiscal 2018 $ 294.1 Fiscal 2019 $ 292.1 Fiscal 2020 $ 281.3 Fiscal 2021 $ 234.6 Fiscal 2022 $ 225.3

Debt

Debt	12 Months Ended
	Sep. 30, 2017
Debt [Abstract]
Debt	Debt In connection with the Combination, the public bonds issued by WestRock RKT Company and WestRock MWV, LLC are guaranteed by WestRock and have cross-guarantees between the two companies. The IDBs associated with the capital lease obligations of WestRock MWV, LLC are guaranteed by WestRock. The public bonds are unsecured, unsubordinated obligations that rank equally in right of payment with all of our existing and future unsecured, unsubordinated obligations. The bonds are effectively subordinated to any of our existing and future secured debt to the extent of the value of the assets securing such debt. At September 30, 2017 , our Credit Facility, Farm Credit Facility and public bonds were unsecured. The following were individual components of debt (in millions): September 30, 2017 September 30, 2016 Carrying Value Weighted Avg Interest Rate Carrying Value Weighted Avg Interest Rate Public bonds due fiscal 2017 to 2022 $ 1,484.5 4.2 % $ 1,651.0 3.9 % Public bonds due fiscal 2023 to 2027 1,368.8 3.6 % 411.8 4.3 % Public bonds due fiscal 2030 to 2033 975.5 5.2 % 987.5 4.7 % Public bonds due fiscal 2037 to 2047 178.8 6.3 % 179.2 6.0 % Term loan facilities 1,622.7 2.5 % 2,195.7 1.8 % Revolving credit facilities 436.4 1.1 % — N/A Receivables-backed financing facility 110.0 2.1 % — N/A Capital lease obligations 177.0 4.3 % 184.4 4.2 % Supplier financing and commercial card programs 130.3 N/A 106.0 N/A International and other debt 70.8 6.8 % 73.6 7.3 % Total debt 6,554.8 3.6 % 5,789.2 3.3 % Less current portion of debt 608.7 292.9 Long-term debt due after one year $ 5,946.1 $ 5,496.3 A portion of the debt classified as long-term, principally our Credit Facility and Receivables Facility, may be paid down earlier than scheduled at our discretion without penalty. Certain restrictive covenants govern our maximum availability under our credit facilities. We test and report our compliance with these covenants as required and were in compliance with all of our covenants at September 30, 2017 . The carrying value of our debt includes the fair value step-up of debt acquired in mergers and acquisitions. At September 30, 2017 , the unamortized fair market value step-up was $281.8 million , which will be amortized over a weighted average remaining life of 12.7 years . The weighted average interest rate also includes the fair value step up. Excluding the step-up, the weighted average interest rate on total debt was 4.1% . At September 30, 2017 , we had $114.6 million of outstanding letters of credit not drawn upon. At September 30, 2017 , we had approximately $2.9 billion of availability under our committed credit facilities and approximately $0.1 billion available under our uncommitted credit facilities. This liquidity, may be used to provide for ongoing working capital needs and for other general corporate purposes including acquisitions, dividends and stock repurchases. The estimated fair value of our debt was approximately $6.8 billion and $6.0 billion as of September 30, 2017 and September 30, 2016 , respectively. The fair value of our long-term debt is primarily either based on quoted prices for those or similar instruments or approximate the carrying amount as the variable interest rates reprice frequently at observable current market rates and are categorized as level 2 within the fair value hierarchy. During fiscal 2017 , 2016 and 2015 amortization of debt issuance costs charged to interest expense were $4.5 million , $4.6 million and $9.3 million , respectively. Public Bonds On August 24, 2017, we issued $500.0 million aggregate principal amount of 3.0% Senior Notes due September 15, 2024 and $500.0 million aggregate principal amount of 3.375% Senior Notes due September 15, 2027 in an unregistered offering pursuant to Rule 144A and Regulation S under the Securities Act at a discount of approximately $1.4 million and $0.2 million , respectively, and recorded debt issuance costs of $4.2 million and $4.3 million , respectively, which are being amortized over the respective terms of the notes. Giving effect to the amortization of the original issue discount and the debt issuance costs, the effective interest rates of the notes are 3.18% and 3.48% , respectively. The proceeds from the issuance of the notes was used to pre-pay $575.0 million of amortization payments through the maturity of our term loan and $415.0 million then outstanding on the Receivables Facility. At September 30, 2017 and September 30, 2016 , the face value of our public bond obligations outstanding were $3.8 billion and $2.9 billion , respectively. Term Loan Facilities and Revolving Credit Facility In connection with the Combination, on July 1, 2015, we entered into the Credit Agreement, which provided for a 5 -year senior unsecured term loan in an aggregate principal amount of $2.3 billion and a 5 -year senior unsecured revolving credit facility in an aggregate committed principal amount of $2.0 billion (together the “ Credit Facility ”). On July 1, 2015, we drew $1.2 billion of the $2.3 billion unsecured term loan and $1.1 billion was available to be drawn on a delayed draw basis not later than April 1, 2016 in up to two separate draws. Certain proceeds of the Credit Facility were used to repay certain indebtedness of our subsidiaries at the time of the Combination, including the then existing RockTenn credit facility, and to pay fees and expenses incurred in connection with the Combination. The Credit Facility is unsecured and is guaranteed by WestRock’s wholly-owned subsidiaries WestRock RKT Company and WestRock MWV, LLC. On March 24, 2016, we drew $600.0 million of the then available $1.1 billion delayed draw term loan facility for general corporate purposes and the balance of the delayed draw term loan facility was terminated. On June 22, 2016, we pre-paid $200.0 million of the term loan amortization payments due through the second quarter of fiscal 2018. On August 24, 2017, in connection with the issuance of public bonds, we pre-paid $575.0 million of the term loan amortization payments due through the maturity of the term loan. The carrying value of this term loan facility at September 30, 2017 and September 30, 2016 was $1,023.5 million and $1,596.7 million , respectively. On July 1, 2016, we executed an option to extend the term of the 5 -year senior unsecured revolving credit facility for one year beyond the original term. On June 30, 2017, we executed an option to extend the term of the facility for a second additional year. Approximately $1.9 billion of the original $2.0 billion aggregate committed principal amount has been extended to July 1, 2022, and the remainder will continue to mature on July 1, 2020. Up to $150 million under the revolving credit facility may be used for the issuance of letters of credit. In addition, up to $400 million of the revolving credit facility may be used to fund borrowings in non-U.S. dollar currencies including Canadian dollars, Euro and Pound Sterling. Additionally, we may request up to $200 million of the revolving credit facility to be allocated to a Mexican peso revolving credit facility. At September 30, 2017 and September 30, 2016 , we had no amounts outstanding under the revolving credit facility. At our option, loans issued under the Credit Facility will bear interest at either LIBOR or an alternate base rate, in each case plus an applicable interest rate margin. Loans will initially bear interest at LIBOR plus 1.125% per annum, in the case of LIBOR borrowings, or at the alternate base rate plus 0.125% per annum, in the alternative, and thereafter the interest rate will fluctuate between LIBOR plus 1.00% per annum and LIBOR plus 1.50% per annum (or between the alternate base rate plus 0.00% per annum and the alternate base rate plus 0.50% per annum), based upon our corporate credit ratings or the leverage ratio (as defined in the Credit Agreement) (whichever yields a lower applicable interest rate margin) at such time. In addition, we will be required to pay fees that will fluctuate between 0.125% per annum to 0.25% per annum on the unused amount of the revolving credit facility, based upon our corporate credit ratings or the leverage ratio (whichever yields a lower fee) at such time. Loans under the Credit Facility may be prepaid at any time without premium. The Credit Agreement contains usual and customary representations and warranties, and usual and customary affirmative and negative covenants, including: financial covenants (including maintenance of a maximum consolidated debt to capitalization ratio and a minimum consolidated interest coverage ratio, as defined in the Credit Agreement) and limitations on liens, additional indebtedness and asset sales and mergers. The Credit Agreement also contains usual and customary events of default, including: non-payment of principal, interest, fees and other amounts; material breach of a representation or warranty; default on other material debt; bankruptcy or insolvency; incurrence of certain material ERISA liabilities; material judgments; impairment of loan documentation; change of control; and material breach of obligations under securitization programs. On July 1, 2015, we entered into the Farm Loan Credit Agreement that provides for a 7 -year senior unsecured term loan in an aggregate principal amount of $600.0 million . The Farm Credit Facility is guaranteed by WestRock, RockTenn and MWV. The carrying value of this facility at September 30, 2017 and September 30, 2016 was $599.2 million and $599.0 million , respectively. On December 1, 2015, we entered into a $200.0 million uncommitted and revolving line of credit with Sumitomo Mitsui Banking Corporation that matured on December 1, 2016. We renewed the facility on February 10, 2017, and it now matures on February 12, 2018. The carrying value of this facility at September 30, 2017 was $106.7 million . At September 30, 2016, we had no amounts outstanding. On February 11, 2016, we entered into a $100.0 million uncommitted and revolving line of credit with the Bank of Tokyo-Mitsubishi UFJ, LTD. The facility matured on February 9, 2017, and was not renewed. At September 30, 2016, we had no amounts outstanding under this facility. On March 4, 2016, we entered into a $100.0 million uncommitted and revolving line of credit with Cooperatieve Rabobank U.A., New York Branch. The facility matured on March 2, 2017 and was renewed as a Euro dollar facility on the same day. The facility is an uncommitted revolving line of credit in the amount of €100.0 million . The facility will be available in Euros only, and continues until terminated in writing by WestRock or the lender. The carrying value of this facility at September 30, 2017 was $118.1 million . At September 30, 2016, we had no amounts outstanding. On May 15, 2017, we entered into a $600.0 million European revolving credit facility with Coöperatieve Rabobank U.A., New York Branch as the administrative agent for the syndicate of banks. This facility provides for a 364-day unsecured Euro and Sterling denominated borrowing of not more than $200.0 million and $400.0 million U.S. dollar equivalent, respectively. The facility matures on May 14, 2018. The carrying value of this facility at September 30, 2017 was $211.6 million . Receivables-Backed Financing Facility We have a $700.0 million Receivables Facility. On July 22, 2016, we extended the maturity date to July 22, 2019. The credit spread for the used portion of the facility is 0.85% . The Receivables Facility includes certain restrictions on what constitutes eligible receivables under the facility and allows for the exclusion of eligible receivables of specific obligors each calendar year subject to the following restrictions: (i) the aggregate of excluded receivables may not exceed 7.5% of eligible receivables under the Receivables Facility, and (ii) the excluded receivables of each obligor may not exceed 2.5% of the aggregate outstanding balance. The borrowing rate, which consists of a blend of the market rate for asset-backed commercial paper and the one month LIBOR rate plus a utilization fee, was 2.2% and 1.4% as of September 30, 2017 and September 30, 2016 , respectively. The commitment fee was 0.25% and 0.25% as of September 30, 2017 and September 30, 2016 , respectively. Borrowing availability under this facility is based on the eligible underlying accounts receivable and compliance with certain covenants. The agreement governing the Receivables Facility contains restrictions, including, among others, on the creation of certain liens on the underlying collateral. We test and report our compliance with these covenants monthly; we were in compliance with all of these covenants at September 30, 2017 . At September 30, 2017 and September 30, 2016 , maximum available borrowings, excluding amounts outstanding under the Receivables Facility, were $577.6 million and $584.3 million , respectively. The carrying amount of accounts receivable collateralizing the maximum available borrowings at September 30, 2017 was approximately $848.3 million . We have continuing involvement with the underlying receivables as we provide credit and collections services pursuant to the Receivables Facility agreement. The carrying value of this facility at September 30, 2017 was $110.0 million . At September 30, 2016, we had no amounts outstanding. Capital Lease and Other Indebtedness The range of due dates on our capital lease obligations are primarily in fiscal 2027 to 2035. Our international debt is primarily in Europe, Brazil and India. See “ Note 23. Subsequent Events (Unaudited) ”. As of September 30, 2017 , the aggregate maturities of debt, excluding capital lease obligations, for the succeeding five fiscal years and thereafter are as follows (in millions): Fiscal 2018 $ 603.6 Fiscal 2019 724.5 Fiscal 2020 1,499.8 Fiscal 2021 — Fiscal 2022 1,000.0 Thereafter 2,309.2 Fair value of debt step-up, deferred financing costs and unamortized bond discounts 240.7 Total $ 6,377.8 As of September 30, 2017 , the aggregate maturities of capital lease obligations for the succeeding five fiscal years and thereafter are as follows (in millions): Fiscal 2018 $ 5.6 Fiscal 2019 4.5 Fiscal 2020 3.4 Fiscal 2021 2.1 Fiscal 2022 2.1 Thereafter 138.7 Fair value step-up 20.6 Total $ 177.0

Fair Value

Fair Value	12 Months Ended
	Sep. 30, 2017
Fair Value [Abstract]
Fair Value	Fair Value Assets and Liabilities Measured or Disclosed at Fair Value We estimate fair values in accordance with ASC 820 “Fair Value Measurement”. ASC 820 provides a framework for measuring fair value and expands disclosures required about fair value measurements. Specifically, ASC 820 sets forth a definition of fair value and a hierarchy prioritizing the inputs to valuation techniques. ASC 820 defines fair value as the price that would be received from the sale of an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Additionally, ASC 820 defines levels within the hierarchy based on the availability of quoted prices for identical items in active markets, similar items in active or inactive markets and valuation techniques using observable and unobservable inputs. We incorporate credit valuation adjustments to reflect both our own nonperformance risk and the respective counterparty’s nonperformance risk in our fair value measurements. We disclose the fair value of our long-term debt in “ Note 11. Debt ” and the fair value of our pension and postretirement assets and liabilities in “ Note 15. Retirement Plans ”. We have, or from time to time may have, various assets or liabilities whose fair values are not significant, such as supplemental retirement savings plans that are nonqualified deferred compensation plans pursuant to which assets are invested primarily in mutual funds, interest rate derivatives, commodity derivatives or other similar classes of assets or liabilities. Accounts Receivable Sales Agreement In fiscal 2014, we entered into an agreement, which has been amended periodically, to sell to a third party financial institution all of the short-term receivables generated from certain customer trade accounts, on a revolving basis, until the agreement is terminated by either party. On June 27, 2016, the A/R Sales Agreement was amended to increase the maximum outstanding balance of receivables available to be sold to $400.0 million . On September 29, 2017, the A/R Sales Agreement was amended to increase the maximum outstanding balance of receivables available to be sold to $490.0 million , and we added new customer trade accounts as well as increased the limits for other customers. Transfers under this agreement meet the requirements to be accounted for as sales in accordance with guidance in ASC 860, “ Transfers and Servicing ”. These customers are not included in the Receivables Facility. The following table represents a summary of the activity under the A/R Sales Agreement for fiscal 2017 and 2016 (in millions): 2017 2016 Receivable from financial institution at beginning of fiscal year $ 13.8 $ 5.8 Receivables sold to the financial institution and derecognized 1,542.5 1,474.6 Receivables collected by financial institution (1,466.7 ) (1,367.2 ) Cash proceeds from financial institution (64.7 ) (99.4 ) Receivable from financial institution at September 30, $ 24.9 $ 13.8 Cash proceeds related to the receivables sold are included in cash from operating activities in the consolidated statement of cash flows in the accounts receivable line item. The loss on sale is not material as it is currently less than 1% per annum of the receivables sold, currently approximately $8 million per fiscal year, and is recorded in interest income and other income (expense), net. Although the sales are made without recourse, we maintain continuing involvement with the sold receivables as we provide collections services related to the transferred assets. The associated servicing liability is not material given the high quality of the customers underlying the receivables and the anticipated short collection period. Financial Instruments not Recognized at Fair Value Financial instruments not recognized at fair value on a recurring or nonrecurring basis include cash and cash equivalents, accounts receivable, certain other current assets, short-term debt, accounts payable, certain other current liabilities, and long-term debt. With the exception of long-term debt, the carrying amounts of these financial instruments approximate their fair values due to their short maturities. See “ Note 11. Debt ” for the fair value of our long-term debt. Fair Value of Nonfinancial Assets and Nonfinancial Liabilities We measure certain nonfinancial assets and nonfinancial liabilities at fair value on a nonrecurring basis. These assets and liabilities include cost and equity method investments when they are deemed to be other-than-temporarily impaired, assets acquired and liabilities assumed in an acquisition or in a nonmonetary exchange, and property, plant and equipment and intangible assets that are written down to fair value when they are held for sale or determined to be impaired. During fiscal 2017 and 2016, we did not have any significant nonfinancial assets or nonfinancial liabilities that were measured at fair value on a nonrecurring basis in periods subsequent to initial recognition other than the $46.7 million real estate impairment recorded in fiscal 2017 in connection with the accelerated monetization strategy in our Land and Development segment, a $17.6 million impairment of a customer relationship intangible in fiscal 2017 related to an exited product line, the goodwill impairment of our former Specialty Chemicals reporting unit in the first quarter of fiscal 2016 and the intangible impairment in the former Specialty Chemicals segment in the third quarter of fiscal 2016 following the Separation. We discuss the former Specialty Chemicals impairments in “ Note 7. Discontinued Operations ”.

Leases

Leases	12 Months Ended
	Sep. 30, 2017
Leases [Abstract]
Leases	Operating Leases We lease certain manufacturing and warehousing facilities and equipment, primarily transportation equipment, and office space under various operating leases. Some leases contain escalation clauses and provisions for lease renewal. As of September 30, 2017 , future minimum lease payments under all noncancelable operating leases for the succeeding five fiscal years and thereafter are as follows (in millions): Fiscal 2018 $ 123.3 Fiscal 2019 103.5 Fiscal 2020 86.3 Fiscal 2021 68.8 Fiscal 2022 54.5 Thereafter 188.6 Total future minimum lease payments $ 625.0 Rental expense for the years ended September 30, 2017 , 2016 and 2015 was approximately $210.5 million , $199.3 million and $144.8 million , respectively, including lease payments under cancelable leases and maintenance charges on transportation equipment.

Income Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2017
Tax Provision [Abstract]
Tax Provision	Income Taxes The components of income (loss) from continuing operations before income taxes are as follows (in millions): Year Ended September 30, 2017 2016 2015 United States $ 481.9 $ (25.1 ) $ 571.3 Foreign 375.7 269.7 162.9 Income from continuing operations before income taxes $ 857.6 $ 244.6 $ 734.2 The loss from continuing operations in the U.S. in fiscal 2016 was primarily the result of the pension risk transfer expense and restructuring charges. See “ Note 15. Retirement Plans ” and “ Note 9. Restructuring and Other Costs, Net ”. Income tax expense (benefit) from continuing operations consists of the following components (in millions): Year Ended September 30, 2017 2016 2015 Current income taxes: Federal $ 80.8 $ 98.3 $ 31.6 State 3.3 12.8 7.3 Foreign 95.3 87.0 38.6 Total current expense 179.4 198.1 77.5 Deferred income taxes: Federal 15.2 (131.5 ) 157.8 State (22.8 ) 6.9 (10.8 ) Foreign (12.8 ) 16.3 8.5 Total deferred (benefit) expense (20.4 ) (108.3 ) 155.5 Total income tax expense $ 159.0 $ 89.8 $ 233.0 The differences between the statutory federal income tax rate and our effective income tax rate from continuing operations are as follows: Year Ended September 30, 2017 2016 2015 Statutory federal tax rate 35.0 % 35.0 % 35.0 % Foreign rate differential (4.9 ) (5.5 ) (1.6 ) Adjustment and resolution of federal, state and foreign tax uncertainties (0.3 ) 0.2 0.3 State taxes, net of federal benefit 3.3 4.9 1.2 Research and development and other tax credits, net of valuation allowances and reserves (0.8 ) (6.1 ) (0.1 ) Income attributable to noncontrolling interest 0.4 0.8 (0.4 ) Domestic manufacturer’s deduction (2.0 ) (4.4 ) (2.6 ) Sale of HH&B (5.0 ) — — U.S. legal entity restructuring (3.3 ) — — Change in valuation allowance (3.3 ) 6.3 (0.8 ) Nondeductible transaction costs 1.0 0.4 1.0 Contribution of assets to Grupo Gondi joint venture — 3.4 — Nontaxable increased cash surrender value (1.5 ) (4.6 ) (0.1 ) Withholding taxes 0.4 2.0 — Brazilian net worth deduction (0.8 ) (2.0 ) (0.1 ) Other, net 0.3 6.3 (0.1 ) Effective tax rate 18.5 % 36.7 % 31.7 % The tax effects of temporary differences that give rise to deferred income tax assets and liabilities consist of the following (in millions): September 30, 2017 2016 Deferred income tax assets: Accruals and allowances $ 40.6 $ 12.2 Employee related accruals and allowances 265.1 217.6 Pension obligations — 15.5 State net operating loss carryforwards 70.6 82.3 State credit carryforwards, net of federal benefit 54.4 56.1 U.S. and foreign tax credit carryforwards 135.9 185.1 Federal and foreign net operating loss carryforwards 204.1 119.3 Restricted stock and options 81.0 94.9 Other 32.8 44.4 Total 884.5 827.4 Deferred income tax liabilities: Property, plant and equipment 2,154.1 2,124.0 Deductible intangibles and goodwill 1,091.4 891.3 Inventory reserves 236.1 205.6 Deferred gain 405.2 432.1 Pension obligations 90.8 — Basis difference in joint ventures 57.1 96.0 Other 8.3 1.0 Total 4,043.0 3,750.0 Valuation allowances 219.1 177.2 Net deferred income tax liability $ 3,377.6 $ 3,099.8 Deferred taxes are recorded as follows in the consolidated balance sheet (in millions): September 30, 2017 2016 Long-term deferred tax asset (1) $ 32.6 $ 30.9 Long-term deferred tax liability 3,410.2 3,130.7 Net deferred income tax liability $ 3,377.6 $ 3,099.8 (1) The long-term deferred tax asset is presented in Other assets on the Consolidated Balance Sheets. At September 30, 2017 and September 30, 2016 , we had gross federal net operating losses of approximately $61.2 million and $85.3 million , respectively. These loss carryforwards generally expire between fiscal 2030 and 2037 . At September 30, 2017 and September 30, 2016 , we had alternative minimum tax credits of $132.2 million and $185.1 million , respectively. Under current tax law, the alternative minimum tax credit carryforwards do not expire. We had research and development tax credits and general business credits of $3.2 million and $0.5 million , respectively, at September 30, 2017. At September 30, 2017 and September 30, 2016 , we had gross state and local net operating losses, of approximately $1,885 million and $1,899 million , respectively. These loss carryforwards generally expire between fiscal 2018 and 2037 . The tax effected values of these net operating losses are $70.6 million and $82.3 million at September 30, 2017 and 2016 , respectively, exclusive of valuation allowances of $15.9 million and $14.2 million at September 30, 2017 and 2016 , respectively. At September 30, 2017 and September 30, 2016 , gross net operating losses for foreign reporting purposes of approximately $673.7 million and $448.7 million , respectively, were available for carryforward. A majority of these loss carryforwards generally expire between fiscal 2018 and 2037 , while a portion have an indefinite carryforward. The tax effected values of these net operating losses are $182.6 million and $119.3 million at September 30, 2017 and 2016 , respectively, exclusive of valuation allowances of $149.6 million and $92.5 million at September 30, 2017 and 2016 , respectively. At September 30, 2017 and 2016 , we had state tax credit carryforwards of $54.4 million and $56.1 million , respectively. These state tax credit carryforwards generally expire within 5 to 10 years; however, certain state credits can be carried forward indefinitely. Valuation allowances of $47.3 million and $51.2 million at September 30, 2017 and 2016 , respectively, have been provided on these assets. These valuation allowances have been recorded due to uncertainty regarding our ability to generate sufficient taxable income in the appropriate taxing jurisdiction. The following table represents a summary of the valuation allowances against deferred tax assets for fiscal 2017 , 2016 and 2015 (in millions): 2017 2016 2015 Balance at beginning of fiscal year $ 177.2 $ 100.2 $ 65.1 Increases 54.3 24.8 2.7 Allowances related to purchase accounting (1) 12.4 63.0 40.0 Reductions (24.8 ) (10.8 ) (7.6 ) Balance at end of fiscal year $ 219.1 $ 177.2 $ 100.2 (1) Adjustments in fiscal 2017 relate to the MPS Acquisition. Adjustments in fiscal 2016 relate to the Combination and the SP Fiber Acquisition. Adjustments in fiscal 2015 relate to the Combination. Consistent with prior years, we consider a portion of our earnings from certain foreign subsidiaries as subject to repatriation and we provide for taxes accordingly. However, we consider the unremitted earnings and all other outside differences from all other foreign subsidiaries to be indefinitely reinvested. Accordingly, we have not provided for any taxes that would be due. As of September 30, 2017 , we estimate our outside basis difference in foreign subsidiaries that are considered indefinitely reinvested to be approximately $2.3 billion . The components of the outside basis difference are comprised of purchase accounting adjustments, undistributed earnings, and equity components. We have not provided for any taxes that would be due upon the reversal of the outside basis differences. However, in the event of a distribution in the form of dividends or dispositions of the subsidiaries, we may be subject to incremental U.S. income taxes, subject to an adjustment for foreign tax credits, and withholding taxes or income taxes payable to the foreign jurisdictions. As of September 30, 2017 , the determination of the deferred tax liability is not practicable. A reconciliation of the beginning and ending amount of gross unrecognized tax benefits is as follows (in millions): 2017 2016 2015 Balance at beginning of fiscal year $ 166.8 $ 106.6 $ 36.5 Additions related to purchase accounting (1) 7.7 16.5 82.9 Additions for tax positions taken in current year 5.0 30.3 2.4 Additions for tax positions taken in prior fiscal years 15.2 20.6 — Reductions for tax positions taken in prior fiscal years (25.6 ) (9.7 ) (3.7 ) Reductions due to settlement (2) (14.1 ) (1.3 ) — Additions (reductions) for currency translation adjustments 2.0 7.0 (11.5 ) Reductions as a result of a lapse of the applicable statute of limitations (8.1 ) (3.2 ) — Balance at end of fiscal year $ 148.9 $ 166.8 $ 106.6 (1) Adjustments in fiscal 2017 relate to the MPS Acquisition. Adjustments in fiscal 2016 relate to the Combination and the SP Fiber Acquisition. Adjustments in fiscal 2015 relate to the Combination. (2) Reductions due to settlement in fiscal 2017 relate to the settlement of federal and state audit examinations with taxing authorities. As of September 30, 2017 and 2016 , the total amount of unrecognized tax benefits was approximately $148.9 million and $166.8 million , respectively, exclusive of interest and penalties. Of these balances, as of September 30, 2017 and 2016 , if we were to prevail on all unrecognized tax benefits recorded, approximately $138.0 million and $138.6 million , respectively, would benefit the effective tax rate. We regularly evaluate, assess and adjust the related liabilities in light of changing facts and circumstances, which could cause the effective tax rate to fluctuate from period to period. We recognize estimated interest and penalties related to unrecognized tax benefits in income tax expense in the consolidated statements of operations. As of September 30, 2017 , we had liabilities of $81.7 million related to estimated interest and penalties for unrecognized tax benefits. As of September 30, 2016 , we had liabilities of $60.2 million , net of indirect benefits, related to estimated interest and penalties for unrecognized tax benefits. Our results of operations for the fiscal year ended September 30, 2017 include expense of $5.4 million related to estimated interest and penalties with respect to the liability for unrecognized tax benefits. Our results of operations for the fiscal years ended September 30, 2016 and 2015 include expense of $7.4 million and $2.9 million , respectively, net of indirect benefits, related to estimated interest and penalties with respect to the liability for unrecognized tax benefits. As of September 30, 2017 , it is reasonably possible that our unrecognized tax benefits will decrease by up to $29.6 million in the next twelve months due to expiration of various statues of limitations and settlement of issues. We file federal, state and local income tax returns in the U.S. and various foreign jurisdictions. With few exceptions, we are no longer subject to U.S. federal and state and local income tax examinations by tax authorities for years prior to fiscal 2014 and fiscal 2007, respectively. We are no longer subject to non-U.S. income tax examinations by tax authorities for years prior to fiscal 2010, except for Brazil for which we are not subject to tax examinations for years prior to 2004. While we believe our tax positions are appropriate, they are subject to audit or other modifications and there can be no assurance that any modifications will not materially and adversely affect our results of operations, financial condition or cash flows.

Retirement Plans

Retirement Plans	12 Months Ended
	Sep. 30, 2017
Retirement Plans [Abstract]
Retirement Plans	Retirement Plans We have defined benefit pension plans and other postretirement benefit plans for certain U.S. and non-U.S. employees. Certain plans were frozen for salaried and non-union hourly employees at various times in the past, although some employees meeting certain criteria are still accruing benefits. In addition, under several labor contracts, we make payments, based on hours worked, into MEPP trusts established for the benefit of certain collective bargaining employees in facilities both inside and outside the U.S. We also have supplemental executive retirement plans and other non-qualified defined benefit pension plans that provide unfunded supplemental retirement benefits to certain of our current and former executives. The supplemental executive retirement plans provide for incremental pension benefits in excess of those offered in the Plan. The other postretirement benefit plans provide certain health care and life insurance benefits for certain salaried and hourly employees who meet specified age and service requirements as defined by the plans. In connection with the Combination, the Rock-Tenn Company Consolidated Pension Plan and MWV U.S. qualified defined benefit pension plans assigned the role of plan sponsor to WestRock. On July 2, 2015, WestRock merged the MWV U.S. qualified defined benefit pension plans into the Rock-Tenn Company Consolidated Pension Plan, and renamed the merged plan the WestRock Company Consolidated Pension Plan. Upon the merger, the terms and provisions of the legacy MWV plans were incorporated into the merged plan. Additionally, on July 30, 2015, WestRock approved changes to freeze the Plan for the remaining U.S. salaried and non-union hourly employees, subject to certain grandfathering. Affected employees accrued a benefit through December 31, 2015, except for employees who receive a benefit under the legacy MWV U.S. qualified defined benefit pension portions of the Plan and who met the criteria for grandfathering. Those employees who met a minimum age of 50 and an aggregate age and service of 75 years or more as of December 31, 2015, are grandfathered and continue to accrue a benefit until December 31, 2020 or their termination date, if earlier. The WestRock retirement program for U.S. salaried and non-union hourly employees in place of the Plan is a defined contribution benefit plan. The benefits under our defined benefit pension plans are based on either compensation or a combination of years of service and negotiated benefit levels, depending upon the plan. We allocate our pension assets to several investment management firms across a variety of investment styles. Our defined benefit Investment Committee meets at least four times a year with our investment advisors to review each management firm’s performance and monitors its compliance with its stated goals, our investment policy and applicable regulatory requirements in the U.S., Canada, and other jurisdictions. Investment returns vary. We believe that, by investing in a variety of asset classes and utilizing multiple investment management firms, we can create a portfolio that yields adequate returns with reduced volatility. Our qualified U.S. plans employ a liability matching strategy augmented with Treasury futures to generally fully hedge against interest rate risk. After we consulted with our actuary and investment advisors, we adopted the target allocations in the table that follows for our pension plans to produce the desired performance. These target allocations are guidelines, not limitations, and occasionally plan fiduciaries will approve allocations above or below target ranges or modify the allocations. Target Allocations U.S. Plans Non-U.S. Plans 2017 2016 2017 2016 Equity investments 15 % 14 % 24 % 28 % Fixed income investments 70 % 71 % 65 % 59 % Short-term investments 1 % 1 % 1 % 1 % Other investments 14 % 14 % 10 % 12 % Total 100 % 100 % 100 % 100 % Our asset allocations by asset category at September 30 were as follows: U.S. Plans Non-U.S. Plans 2017 2016 2017 2016 Equity investments 13 % 15 % 26 % 29 % Fixed income investments 73 % 66 % 64 % 59 % Short-term investments 3 % 7 % 3 % 2 % Other investments 11 % 12 % 7 % 10 % Total 100 % 100 % 100 % 100 % We manage our retirement plans in accordance with the provisions of ERISA as well as applicable legislation in Canada and other foreign countries. Our investment policy objectives include maximizing long-term returns at acceptable risk levels, diversifying among asset classes, as applicable, and among investment managers, as well as establishing certain risk parameters within asset classes. We have allocated our investments within the equity and fixed income asset classes to sub-asset classes designed to meet these objectives. In addition, our other investments support multi-strategy objectives. In developing our weighted average expected rate of return on plan assets, we consulted with our investment advisors and evaluated criteria based on historical returns by asset class and long-term return expectations by asset class. We use a September 30 measurement date. We expect to contribute approximately $39 million to our U.S. and non-U.S. pension plans in fiscal 2018 , primarily related to our Canadian plans. However, it is possible that our assumptions or legislation may change, actual market performance may vary or we may decide to contribute a different amount. Therefore, the amount we contribute may vary materially. The expense for MEPPs for collective bargaining employees generally equals the contributions for these plans. The weighted average assumptions used to measure the benefit plan obligations at September 30, were: Pension Plans 2017 2016 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Discount rate 4.09% 3.26% 4.04% 3.08 % Rate of compensation increase 3.00% 3.17% 3.00% 3.09 % We determine the discount rate with the assistance of actuaries. At September 30, 2017 , the discount rate for the U.S. pension plans was determined based on the yield on a theoretical portfolio of high-grade corporate bonds, and the discount rate for the non-U.S. plans was determined based on a yield curve developed by our actuary. The theoretical portfolio of high-grade corporate bonds used to select the September 30, 2017 discount rate for the U.S. pension plans includes bonds generally rated Aa- or better with at least $100 million outstanding par value and bonds that are non-callable (unless the bonds possess a “make whole” feature). The theoretical portfolio of bonds has cash flows that generally match our expected benefit payments in future years. Our assumption regarding the future rate of compensation increases is reviewed periodically and is based on both our internal planning projections and recent history of actual compensation increases. We typically review our expected long-term rate of return on plan assets periodically through an asset allocation study with either our actuary or investment advisor. In fiscal 2018, our expected rate of return used to determine net periodic benefit cost is 6.50% for our U.S. plans and 4.98% for our non-U.S. plans. Our expected rates of return in fiscal 2018 are based on an analysis of our long-term expected rate of return and our current asset allocation. During the second quarter of fiscal 2017, our year-to-date lump sum payments to certain beneficiaries of the Plan, together with several one-time severance benefit payments out of the Plan, triggered pension settlement accounting and a remeasurement of the Plan as of February 28, 2017. As a result of settlement accounting, we recognized as a current period expense a pro-rata portion of the unamortized net actuarial loss, after remeasurement, and recorded a $28.7 million non-cash charge to our earnings in the second quarter of 2017. The lump sum payments were to certain eligible former employees who were not currently receiving a monthly benefit. Eligible former employees whose present value of future pension benefits exceeded a certain minimum threshold had the option to either voluntarily accept lump sum payments or to not accept the offer and continue to be entitled to their monthly benefit upon retirement. Lump sum and one-time severance benefits payments of $203.7 million were made out of existing assets of the Plan in the first half of fiscal 2017. The discount rate used in the plan remeasurement was 4.49% , an increase from 4.04% for the Plan at September 30, 2016. The expected long-term rate of return on plan assets was unchanged. As a result of the February 28, 2017 remeasurement, the funded status of the Plan increased by $73.2 million as compared to September 30, 2016. The increase in the funded status was primarily due to a reduction in the plan obligations due to the increase in the discount rate. In the second half of fiscal 2017, we made $ 27.1 million in lump sum payments to certain beneficiaries of the Plan, resulting in total fiscal 2017 lump sum payments of $230.8 million and a total fiscal 2017 non-cash charge to our earnings of $32.6 million . On September 21, 2016, we used plan assets to settle $2.5 billion in pension obligations of the Plan by purchasing group annuity contracts from Prudential. This transaction transferred payment responsibility to Prudential for retirement benefits owed to approximately 35,000 U.S. retirees and their beneficiaries. As a result of the transaction, we recorded a non-cash charge of $370.7 million pre-tax. The settlement reduced our overall U.S. pension obligations and assets by approximately 40% . The monthly retirement benefit payment amounts currently received by retirees and their beneficiaries did not change as a result of this transaction. Those Plan participants not included in the transaction remain in the Plan, and responsibility for payment of the retirement benefits remains with us. During the first quarter of fiscal 2015, we partially settled obligations of one of our qualified defined benefit pension plans through lump sum payments to certain eligible former employees who were not currently receiving a monthly benefit. Eligible former employees whose present value of future pension benefits exceeded a certain minimum threshold had the option to either voluntarily accept lump sum payments or to not accept the offer and continue to be entitled to their monthly benefit upon retirement. Former employees with an aggregate pension benefit obligation of $163.7 million accepted the offer. Lump sum payments of $135.1 million were made out of existing plan assets. The settlement resulted in a gain of $28.6 million that was more than offset by the loss on remeasurement of the pension benefit obligation of approximately $32.5 million due primarily to the impact of a lower discount rate and mortality table changes. As a result, we recorded a net $3.9 million loss to other comprehensive income. The settlement also resulted in a $20.0 million pre-tax non-cash charge to earnings, which is included in the line item “Pension lump sum settlement and retiree medical curtailment, net” on our Consolidated Statements of Operations. The impact of the settlement is included in the net periodic pension cost table below. As a result of the remeasurement, the pension benefit obligation increased $22.1 million due to changes in coverage for certain employees covered by the USW master agreement as discussed below, with an offset recorded to the unrecognized prior service cost component of other comprehensive income. In the first quarter of fiscal 2015, we entered into a master agreement with the USW that applied to substantially all of our legacy RockTenn facilities where employees that they represent are employed. The agreement has a six year term and covers a number of specific items such as wages, medical coverage and certain other benefit programs. Individual facilities will continue to have local agreements for subjects not covered by the USW master agreement and those agreements will continue to have staggered terms. The following table shows the changes in benefit obligation and plan assets, and the plan’s funded status for the years ended September 30 (in millions): Pension Plans 2017 2016 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Change in projected benefit obligation Benefit obligation at beginning of fiscal year $ 4,231.7 $ 925.2 $ 6,122.3 $ 865.1 Service cost 38.0 7.1 45.7 5.7 Interest cost 165.2 32.6 277.8 32.5 Amendments 3.5 — 1.4 — Actuarial (gain) loss (149.1 ) (57.6 ) 664.2 70.8 Plan participant contributions — 1.7 — 1.5 Special termination benefits 12.5 — 18.4 — Benefits paid (141.4 ) (65.1 ) (399.2 ) (57.5 ) Business combinations — 621.0 9.9 (0.6 ) Curtailments — — (2.7 ) (0.5 ) Settlements (229.3 ) (0.4 ) (2,484.6 ) (0.1 ) Foreign currency rate changes — 65.1 — 8.3 Other adjustments 10.8 — — — Business divestitures — (27.4 ) (21.5 ) — Benefit obligation at end of fiscal year $ 3,941.9 $ 1,502.2 $ 4,231.7 $ 925.2 Change in plan assets Fair value of plan assets at beginning of fiscal year $ 4,301.5 $ 774.1 $ 6,481.6 $ 711.8 Actual gain on plan assets 104.2 2.4 707.3 82.9 Employer contributions 15.3 19.2 16.1 31.4 Plan participant contributions — 1.7 — 1.5 Benefits paid (141.4 ) (65.1 ) (399.2 ) (57.5 ) Business combinations — 622.1 — — Settlements (229.3 ) (0.4 ) (2,484.6 ) (0.1 ) Business divestitures — (0.7 ) (19.7 ) — Foreign currency rate changes — 61.4 — 4.1 Other adjustments 57.6 — — — Fair value of plan assets at end of fiscal year $ 4,107.9 $ 1,414.7 $ 4,301.5 $ 774.1 Funded status $ 166.0 $ (87.5 ) $ 69.8 $ (151.1 ) Amounts recognized in consolidated balance sheet: Non-current assets $ 340.4 $ 27.6 $ 247.3 $ 10.5 Other current liability (9.3 ) (0.8 ) (9.9 ) (1.1 ) Accrued pension and other long-term benefits (165.1 ) (114.3 ) (167.6 ) (160.5 ) Over (under) funded status at end of fiscal year $ 166.0 $ (87.5 ) $ 69.8 $ (151.1 ) Although the U.S. pension plans were in a net over funded position at September 30, 2017 , certain U.S. plans have benefit obligations in excess of plan assets. These plans have aggregate projected benefit obligations of $204.6 million , aggregate accumulated benefit obligations of $201.9 million , and aggregate fair value of plan assets of $30.2 million at September 30, 2017 . The accumulated benefit obligation of U.S. and non-U.S. pension plans was $5,390.7 million and $5,112.0 million at September 30, 2017 and 2016 , respectively. The pre-tax amounts in accumulated other comprehensive loss at September 30 not yet recognized as components of net periodic pension cost, including noncontrolling interest, consist of (in millions): Pension Plans 2017 2016 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Net actuarial loss $ 547.3 $ 173.9 $ 633.4 $ 195.8 Prior service cost 27.6 0.4 28.2 0.4 Total accumulated other comprehensive loss $ 574.9 $ 174.3 $ 661.6 $ 196.2 The pre-tax amounts recognized in other comprehensive (income) loss, including noncontrolling interest, are as follows at September 30 (in millions): Pension Plans 2017 2016 2015 Net actuarial (gain) loss arising during period $ (48.8 ) $ 355.4 $ 85.9 Amortization and settlement recognition of net actuarial loss (57.7 ) (381.6 ) (49.2 ) Prior service cost arising during period 3.4 1.5 26.4 Amortization of prior service cost (4.1 ) (3.9 ) (3.0 ) Net other comprehensive (income) loss recognized $ (107.2 ) $ (28.6 ) $ 60.1 The net periodic pension cost recognized in the consolidated statements of operations is comprised of the following for fiscal years ended (in millions): Pension Plans 2017 2016 2015 Service cost $ 45.1 $ 51.4 $ 44.7 Interest cost 197.8 310.3 218.1 Expected return on plan assets (313.1 ) (412.3 ) (292.9 ) Amortization of net actuarial loss 25.4 11.0 29.0 Amortization of prior service cost 4.1 3.9 3.0 Curtailment gain — (1.6 ) — Settlement loss 32.7 370.7 20.2 Special termination benefits 12.5 18.4 9.1 Company defined benefit plan expense 4.5 351.8 31.2 Multiemployer and other plans 4.7 5.8 5.6 Net pension cost $ 9.2 $ 357.6 $ 36.8 The fiscal 2017, 2016 and 2015 special termination benefits were recorded to restructuring in connection with the Combination, and should be excluded from the calculation of pension funding more than expense. Weighted-average assumptions used in the calculation of benefit plan expense for fiscal years ended: Pension Plans 2017 2016 2015 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Discount rate 4.30% 3.08 % 4.70 % 3.89 % 4.52 % 4.00 % Rate of compensation increase 3.00% 3.09 % 2.50 % 3.10 % 2.54 % 3.00 % Expected long-term rate of return on plan assets 6.50% 6.03 % 5.88 % 6.34 % 7.11 % 6.88 % In fiscal 2017, 2016 and 2015, for our U.S. pension and postretirement plans, we considered the mortality tables from the Society of Actuaries and evaluated our mortality experience to establish mortality assumptions. Based on our experience and in consultation with our actuaries, we utilized the base RP-2014 mortality tables with a gender and job classification specific increase, and applied an improvement scale with generational improvements that is generally based on Social Security Administration analysis and assumptions. The increases for fiscal 2017 are 9% for white collar males, 12% for blue collar males, 11% for white collar females, and 9% for blue collar females. The increases for fiscal 2016 were 6% for white collar males, 10% for blue collar males, 12% for white collar females, and 19% for blue collar females. The increases for fiscal 2015 were 6% for all males, 13% for white collar females, and 19% for blue collar females. In fiscal 2017, 2016 and 2015 our Canadian pension and postretirement plans utilized the 2014 Private Sector Canadian Pensioners Mortality Table adjusted to reflect industry and our mortality experience and applied Canadian Pensioner’s Mortality Improvement Scale B with generational improvements. The estimated losses that will be amortized from accumulated other comprehensive loss into net periodic benefit cost in fiscal 2018 are as follows (in millions): Pension Plans U.S. Plans Non-U.S. Plans Actuarial loss $ 12.2 $ 6.2 Prior service cost 4.3 0.1 Total $ 16.5 $ 6.3 Our projected estimated benefit payments (unaudited), which reflect expected future service, as appropriate, are as follows (in millions): Pension Plans U.S. Plans Non-U.S. Plans Fiscal 2018 $ 200.5 $ 82.2 Fiscal 2019 $ 206.8 $ 82.6 Fiscal 2020 $ 217.9 $ 81.7 Fiscal 2021 $ 222.6 $ 81.9 Fiscal 2022 $ 213.1 $ 81.9 Fiscal Years 2023 – 2027 $ 1,146.5 $ 408.4 The following table summarizes our pension plan assets measured at fair value on a recurring basis (at least annually) as of September 30, 2017 (in millions): Total Quoted Prices Significant Equity securities: U.S. equities (1) $ 136.7 $ 136.6 $ 0.1 Non-U.S. equities (1) 40.0 40.0 — Fixed income securities: U.S. government securities (2) 452.0 — 452.0 Non-U.S. government securities (3) 130.0 — 130.0 U.S. corporate bonds (3) 1,515.4 92.3 1,423.1 Non-U.S. corporate bonds (3) 373.7 51.1 322.6 Mortgage-backed securities (3) 0.1 — 0.1 Other fixed income (4) 311.4 — 311.4 Short-term investments (5) 184.6 184.6 — Benefit plan assets measured in the fair value hierarchy $ 3,143.9 $ 504.6 $ 2,639.3 Assets measured at NAV (6) 2,378.7 Total benefit plan assets $ 5,522.6 The following table summarizes our pension plan assets measured at fair value on a recurring basis (at least annually) as of September 30, 2016 (in millions): Total Quoted Prices Significant Equity securities: U.S. equities (1) $ 192.7 $ 192.7 $ — Non-U.S. equities (1) 74.1 73.5 0.6 Fixed income securities: U.S. government securities (2) 1,271.1 — 1,271.1 Non-U.S. government securities (3) 93.4 5.3 88.1 U.S. corporate bonds (3) 616.9 9.0 607.9 Non-U.S. corporate bonds (3) 255.2 6.4 248.8 Mortgage-backed securities (3) 2.4 — 2.4 Other fixed income (4) 317.5 — 317.5 Short-term investments (5) 302.1 302.1 — Benefit plan assets measured in the fair value hierarchy $ 3,125.4 $ 589.0 $ 2,536.4 Assets measured at NAV (6) 1,950.2 Total benefit plan assets $ 5,075.6 (1) Equity securities are comprised of the following investment types: (i) common stock, (ii) preferred stock and (iii) equity exchange traded funds. Level 1 investments in common and preferred stocks and exchange traded funds are valued using quoted market prices multiplied by the number of shares owned. (2) U.S. government securities include treasury and agency debt. These investments are valued using broker quotes in an active market. (3) The level 1 non-U.S. government securities investment is an exchange traded fund valued using quoted market prices. The level 1 U.S. corporate bonds category is primarily comprised of U.S. dollar denominated investment grade securities and valued using quoted market prices. Level 2 investments are valued utilizing a market approach that includes various valuation techniques and sources such as value generation models, broker quotes in active and non-active markets, benchmark yields and securities, reported trades, issuer spreads, and/or other applicable reference data. (4) Other fixed income is comprised of municipal and asset-backed securities. Investments are valued utilizing a market approach that includes various valuation techniques and sources, such as broker quotes in active and non-active markets, benchmark yields and securities, reported trades, issuer spreads and/or other applicable reference data. (5) Short-term investments are valued at $1.00/unit, which approximates fair value. Amounts are generally invested in interest-bearing accounts. (6) Investments that are measured at NAV (or its equivalent) as a practical expediency have not been classified in the fair value hierarchy. The following table summarizes assets measured at fair value based on NAV per share as a practical expedient as of September 30, 2017 and 2016 (in millions): Fair value Redemption Frequency Redemption Notice Period Unfunded Commitments September 30, 2017 Hedge funds (1) $ 64.2 Quarterly Up to 91 days $ — Commingled funds, private equity and private real estate investments, and equity related investments (2) 1,207.6 Monthly Up to 60 days 98.8 Fixed income and fixed income related instruments (3) 1,106.9 Monthly Up to 10 days — $ 2,378.7 $ 98.8 September 30, 2016 Hedge funds (1) $ 265.7 Quarterly Up to 91 days $ — Commingled funds, private equity, private real estate investments, and equity related investments (2) 881.3 Monthly Up to 60 days 123.6 Fixed income and fixed income related instruments (3) 744.1 Monthly Up to 10 days — Other (4) 59.1 Daily Up to 5 days — $ 1,950.2 $ 123.6 (1) Hedge fund investments are primarily made through shares of limited partnerships or similar structures. Hedge funds are typically valued monthly by third-party administrators that have been appointed by the funds’ general partners. Hedge funds have been valued using NAV as a practical expedient. (2) Commingled fund investments are valued at the net asset value per share multiplied by the number of shares held. The determination of net asset value for the commingled funds includes market pricing of the underlying assets as well as broker quotes and other valuation techniques. Commingled funds have been valued using NAV as a practical expedient. We maintain holdings in certain private equity partnerships and private real estate investments for which a liquid secondary market does not exist. The private equity partnerships are commingled investments. Valuation techniques, such as discounted cash flow and market based comparable analyses, are used to determine fair value of the private equity investments. Unobservable inputs used for the discounted cash flow technique include projected future cash flows and the discount rate applied to present value those cash flows. Unobservable inputs used for the market based comparisons technique include EBITDA multiples in other comparable third-party transactions, price to earnings ratios, liquidity, current operating results, as well as input from general partners and other pertinent information. Private equity investments have been valued using NAV as a practical expedient. Private real estate investments are commingled investments. Valuation techniques, such as discounted cash flow and market based comparable analyses, are used to determine fair value of the private equity investments. Unobservable inputs used for the discounted cash flow technique include projected future cash flows and the discount rate applied to present value those cash flows. Unobservable inputs used for the market based comparison technique include a combination of third party appraisals, replacement cost, and comparable market prices. Private real estate investments have been valued using NAV as a practical expedient. Equity related investments are hedged equity investments in a commingled fund that consist primarily of equity indexed investments which are hedged by options and also hold collateral in the form of short term treasury securities. Equity related investments have been valued using NAV as a practical expedient. (3) Fixed income and fixed income related instruments consist of commingled debt funds, which are valued at their net asset value per share multiplied by the number of shares held. The determination of net asset value for the commingled funds includes market pricing of the underlying assets as well as broker quotes and other valuation techniques. Commingled debt funds have been valued using NAV as a practical expedient. (4) Consists of a global multi-asset investment commingled fund with underlying investments that are diversified across multiple asset classes and include global equity, fixed income securities, commodities and derivative contracts. The commingled fund is valued at its net asset value per share multiplied by the number of shares held. The determination of net asset value for the commingled fund includes market pricing of the underlying assets as well as broker quotes and other valuation techniques. The global multi-asset investment commingled fund has been valued using NAV as a practical expedient. Postretirement Plans The postretirement benefit plans provide certain health care and life insurance benefits for certain salaried and hourly employees who meet specified age and service requirements as defined by the plans. During the first quarter of fiscal 2015, changes in retiree medical coverage for certain employees covered by the USW master agreement resulted in the recognition of an estimated $8.1 million pre-tax non-cash curtailment gain included in the line item “Pension lump sum settlement and retiree medical curtailment, net” on our Consolidated Statements of Operations, which was subsequently adjusted in the third quarter of fiscal 2015 to $8.5 million . The aggregate postretirement benefit obligation decreased $0.6 million as a result of the curtailment. The weighted average assumptions used to measure the benefit plan obligations at September 30 were: Postretirement plans 2017 2016 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Discount rate 4.09% 6.51 % 4.04% 6.64 % Rate of compensation increase N/A 7.37 % N/A 3.14 % The following table shows the changes in benefit obligation and plan assets, and the plan’s funded status for the years ended September 30 (in millions): Postretirement Plans 2017 2016 Change in projected benefit obligation U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Benefit obligation at beginning of fiscal year $ 90.7 $ 62.6 $ 109.5 $ 51.6 Service cost 0.1 0.8 1.7 0.6 Interest cost 3.3 4.1 4.5 3.6 Amendments (3.4 ) (1.0 ) (4.0 ) — Actuarial loss (gain) 14.1 0.4 (6.3 ) 5.0 Benefits paid (8.0 ) (2.7 ) (14.1 ) (2.5 ) Business combinations 1.3 2.0 — — Business divestitures — (0.4 ) (0.6 ) — Curtailments — (0.3 ) — — Foreign currency rate changes — 2.6 — 4.3 Benefit obligation at end of fiscal year $ 98.1 $ 68.1 $ 90.7 $ 62.6 Change in plan assets Fair value of plan assets at beginning of fiscal year $ — $ — $ — $ — Employer contributions 8.0 2.7 14.1 2.5 Plan participant contributions — — — — Benefits paid (8.0 ) (2.7 ) (14.1 ) (2.5 ) Fair value of plan assets at end of fiscal year $ — $ — $ — $ — Funded Status $ 98.1 $ 68.1 $ 90.7 $ 62.6 Amounts recognized in the consolidated balance sheet: Other current liability $ (9.8 ) $ (3.0 ) $ (10.4 ) $ (2.9 ) Accrued postretirement and other long-term benefits (88.3 ) (65.1 ) (80.3 ) (59.7 ) Under funded status at end of fiscal year $ (98.1 ) $ (68.1 ) $ (90.7 ) $ (62.6 ) The pre-tax amounts in accumulated other comprehensive loss at September 30 not yet recognized as components of net periodic postretirement cost, including noncontrolling interest, consist of (in millions): Postretirement Plans 2017 2016 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Net actuarial (gain) loss $ (9.1 ) $ 4.2 $ (24.9 ) $ 4.1 Prior service credit (13.9 ) (1.4 ) (14.9 ) (0.4 ) Total accumulated other comprehensive (income) loss $ (23.0 ) $ 2.8 $ (39.8 ) $ 3.7 The pre-tax amounts recognized in other comprehensive loss (income), including noncontrolling interest, are as follows at September 30 (in millions): Postretirement Plans 2017 2016 2015 Net actuarial loss (gain) arising during period $ 14.7 $ (1.4 ) $ (4.4 ) Amortization and settlement recognition of net actuarial gain 1.3 1.9 1.1 Prior service credit arising during period (4.4 ) (3.8 ) (1.4 ) Amortization or curtailment recognition of prior service credit 4.5 2.1 10.5 Net other comprehensive loss (income) recognized $ 16.1 $ (1.2 ) $ 5.8 The net periodic postretirement cost recognized in the consolidated statements of operations is comprised of the following for fiscal years ended (in millions): Postretirement Plans 2017 2016 2015 Service cost $ 0.9 $ 2.3 $ 1.0 Interest cost 7.4 8.1 5.4 Amortization of net actuarial gain (1.3 ) (2.0 ) (1.1 ) Amortization of prior service credit (4.5 ) (2.1 ) (2.0 ) Curtailment gain (0.3 ) — (8.5 ) Net postretirement cost (credit) $ 2.2 $ 6.3 $ (5.2 ) The assumed health care cost trend rates used in measuring the APBO are as follows at September 30: 2017 U.S. Plans Health care cost trend rate assumed for next year 6.29 % Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) 4.43 % Year the rate reaches the ultimate trend rate 2037 Non-U.S. Plans Health care cost trend rate assumed for next year 7.27 % Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) 6.16 % Year the rate reaches the ultimate trend rate 2029 As of September 30, 2017 , the effect of a 1% change in the assumed health care cost trend rate would increase the APBO by approximately $10 million and decrease the APBO by approximately $8 million , and would increase and decrease the annual net periodic postretirement benefit cost for fiscal 2017 by approximately $1 million . Weighted-average assumptions used in the calculation of benefit plan expense for fiscal years ended: Postretirement Plans 2017 2016 2015 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Discount rate 4.04% 6.64 % 4.70% 6.84 % 4.52 % 4.00 % Rate of compensation increase N/A 3.14 % N/A 3.10 % N/A 3.00 % The estimated (gains) losses that will be amortized from accumulated other comprehensive loss into net periodic benefit cost in fiscal 2018 are as follows (in millions): Postretirement Plans U.S. Plans Non-U.S. Plans Actuarial (gain) loss $ (0.9 ) $ 0.7 Prior service credit (4.0 ) (0.2 ) Total $ (4.9 ) $ 0.5 Our projected estimated benefit payments (unaudited), which reflect expected future service, as appropriate, are as follows (in millions): Postretirement Plans U.S. Plans Non-U.S. Plans Fiscal 2018 $ 9.8 $ 3.0 Fiscal 2019 $ 8.6 $ 3.1 Fiscal 2020 $ 8.0 $ 3.2 Fiscal 2021 $ 7.6 $ 3.3 Fiscal 2022 $ 7.3 $ 3.3 Fiscal Years 2023 – 2027 $ 32.1 $ 18.3 Multiemployer Plans We participate in several MEPPs that provide retirement benefits to certain union employees in accordance with various CBAs. The risks of participating in MEPPs are different from the risks of participating in single-employer pension plans. These risks include: • assets contributed to a MEPP by one employer are used to provide benefits to employees of all participating employers, • if a participating employer withdraws from a MEPP, the unfunded obligations of the MEPP allocable to such withdrawing employer may be borne by the remaining participating employers and • if we withdraw from a MEPP, we may be required to pay that plan an amount based on our allocable share of the unfunded vested benefits of the plan, referred to as a withdrawal liability, as well as a share of the MEPP’s accumulated funding deficiency. Our contributions to a parti

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Sep. 30, 2017
Shareholders’ Equity [Abstract]
Shareholders' Equity	Stockholders’ Equity Capitalization Our capital stock consists solely of Common Stock. Holders of our Common Stock are entitled to one vote per share. Our amended and restated certificate of incorporation also authorizes preferred stock, of which no shares have been issued. The terms and provisions of such shares will be determined by our board of directors upon any issuance of such shares in accordance with our certificate of incorporation. Stock Repurchase Plan In July 2015, our board of directors authorized a repurchase program of up to 40.0 million shares of our Common Stock, representing approximately 15% of our outstanding Common Stock as of July 1, 2015. The shares of our Common Stock may be repurchased over an indefinite period of time at the discretion of management. In fiscal 2017, we repurchased approximately 1.8 million shares of our Common Stock for an aggregate cost of $93.0 million . In fiscal 2016, we repurchased approximately 8.1 million shares of our Common Stock for an aggregate cost of $335.3 million . Subsequent to the authorization, in the fourth quarter of fiscal 2015, we repurchased approximately 5.4 million shares of our Common Stock for an aggregate cost of $328.0 million . Separately, as part of the Combination, RockTenn repurchased 10.5 million shares of RockTenn Common Stock for an aggregate cost of $667.8 million . Prior to the closing of the Combination and pursuant to the then existing RockTenn repurchase plan, in the first quarter of fiscal 2015, RockTenn repurchased 0.2 million shares of RockTenn Common Stock for an aggregate cost of $8.7 million . As of September 30, 2017 , we had remaining authorization under the repurchase program authorized in July 2015 to purchase approximately 24.7 million shares of our Common Stock.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Sep. 30, 2017
Stock Based Compensation [Abstract]
Stock Based Compensation	Share-Based Compensation Share-based Compensation Plans At our Annual Meeting of Stockholders held on February 2, 2016, our stockholders approved the 2016 Incentive Stock Plan and the ESPP Plan. The 2016 Incentive Stock Plan allows for the granting of options, restricted stock, SARs and restricted stock units to certain key employees and directors for the issuance of up to 9.6 million shares of Common Stock. Adjusted for the Separation as discussed below, at September 30, 2017 , approximately 6.9 million shares remained available for future grants. If all currently outstanding restricted stock awards granted with a performance condition recorded at target achieve the maximum award, shares available for future grant would be reduced by approximately 2.0 million additional shares. The ESPP provides for the purchase of shares by all of our eligible employees at a 15% discount and allowed for the purchase of a total of up to 2.5 million shares of Common Stock. As of September 30, 2017 , adjusted for the Separation, approximately 2.6 million shares of Common Stock remained available for purchase under the ESPP. In connection with the Combination, WestRock assumed all RockTenn and MWV equity incentive plans. We issue nonqualified stock options and restricted stock to certain key employees and our directors pursuant to our RockTenn 2004 Incentive Stock Plan, as amended, and our MWV 2005 Performance Incentive Plan, as amended. The RockTenn 2004 Incentive Stock Plan allows for the granting of options, restricted stock, SARs and restricted stock units to certain key employees and directors for the issuance of approximately 15.8 million shares of Common Stock. At the time of the Combination, all outstanding RockTenn awards were converted to WestRock awards with no conversion factor. Adjusted for the Separation as discussed below, at September 30, 2017 , approximately 3.1 million shares remained available for the future grant of awards. If all currently outstanding restricted stock awards subject to performance criteria recorded at target achieve the maximum award, shares available for future grant would be reduced by approximately 0.4 million additional shares. However, we have determined that we will not make any new grants of awards pursuant to the RockTenn 2004 Incentive Stock Plan. In connection with the Combination, we assumed the MWV 2005 Performance Incentive Plan. The MWV shares available for issuance, stock options, SARs and unvested restricted stock units outstanding at the time of the Combination under the MWV 2005 Performance Incentive Plan were converted into WestRock options, SARs and restricted stock units, as applicable, with respect to shares of our Common Stock using the conversion factor as described in the Business Combination Agreement. The number of shares available under this plan upon conversion was approximately 12.8 million shares. Adjusted for the Separation as discussed below, at September 30, 2017 , approximately 8.9 million shares remained available for future grants. If all currently outstanding restricted stock awards granted with a performance condition recorded at target achieve the maximum award, shares available for future grant would be reduced by approximately 0.1 million additional shares. However, we have determined that we will not make any new grants of awards pursuant to the MWV 2005 Performance Incentive Plan. In connection with the Smurfit-Stone Acquisition, we assumed the Smurfit-Stone equity incentive plan, which was renamed the Rock-Tenn Company (SSCC) Equity Incentive Plan. The shares available for issuance, stock options and unvested restricted stock units outstanding at the time of the Smurfit-Stone Acquisition, under the Smurfit-Stone plan were converted into shares of RockTenn Common Stock, options and restricted stock units, as applicable, using the conversion factor as described in the merger agreement. The number of shares available under this plan upon conversion was approximately 7.9 million shares. Adjusted for the Separation as discussed below, at September 30, 2017 , approximately 5.9 million shares remained available for future grants exclusively to legacy Smurfit-Stone employees who have continued employment with WestRock; however, we have determined that we will not make any new grants of awards pursuant to the Rock-Tenn Company (SSCC) Equity Incentive Plan. As part of the Separation, equity-based incentive awards were generally adjusted to maintain the intrinsic value of awards immediately prior to the Separation. The number of unvested restricted stock awards and unexercised stock options and SARs at the time of the Separation were increased by an exchange factor of approximately 1.12 . In addition, the exercise price of unexercised stock options and SARs at the time of the Separation was converted to decrease the exercise price by an exchange factor of approximately 1.12 . Our results of operations for the fiscal years ended September 30, 2017 , 2016 and 2015 include share-based compensation expense of $60.9 million , $75.7 million and $49.2 million , respectively, including $2.9 million included in the gain on sale of HH&B. Share-based compensation expense in fiscal 2017 was reduced by $5.4 million for the rescission of shares granted to our CEO that were inadvertently granted in excess of plan limits in fiscal 2014 and 2015. The total income tax benefit in the results of operations in connection with share-based compensation was $22.5 million , $29.2 million and $19.0 million , for the fiscal years ended September 30, 2017 , 2016 and 2015 , respectively. ASC 718 requires that the benefits of tax deductions in excess of recognized compensation cost are reported as a financing cash flow. Excess tax benefits of approximately $6.7 million , $0.3 million and $23.0 million were included in cash used for financing activities in fiscal 2017 , 2016 and 2015 , respectively. Cash received from share-based payment arrangements for the fiscal years ended September 30, 2017 , 2016 and 2015 was $59.2 million , $33.9 million and $27.2 million , respectively. Equity Awards Issued in Connection with the MPS Acquisition In connection with the MPS Acquisition, we replaced certain outstanding awards of restricted stock units granted under the MPS long-term incentive plan with WestRock restricted stock units. No additional shares will be granted under the MPS plan. The MPS equity awards were replaced with identical terms utilizing an approximately 0.33 conversion factor as described in the merger agreement. As part of the MPS Acquisition, we granted 119,373 awards of restricted stock units, which contain service conditions and were valued at $54.24 per share. The acquisition consideration included approximately $1.9 million related to outstanding MPS equity awards related to service prior to the effective date of the merger – the balance related to service after the effective date will be expensed over the remaining service period of the awards. Equity Awards Issued in Connection with the Combination Included in the fiscal 2015 merger consideration was approximately $210.9 million related to outstanding MWV equity awards that were replaced with WestRock equity awards with identical terms for pre-Combination service utilizing a 0.78 conversion factor. The amount related to post-Combination service will be expensed over the remaining service period of the awards. The primary components of the employee awards are discussed below. Stock Options and Stock Appreciation Rights Stock options granted under our plans generally have an exercise price equal to the closing market price on the date of the grant, generally vest in three years, in either one tranche or in approximately one-third increments, and have 10 -year contractual terms. However, a portion of our grants are subject to earlier expense recognition due to retirement eligibility rules. Presently, other than circumstances such as death, disability and retirement, grants will include a provision requiring both a change of control and termination of employment to accelerate vesting. At the date of grant, we estimate the fair value of stock options granted using a Black-Scholes option pricing model. We use historical data to estimate option exercises and employee terminations in determining the expected term in years for stock options. Expected volatility is calculated based on the historical volatility of our stock, or a combination of the historical volatility of both RockTenn and MWV grants. The risk-free interest rate is based on U.S. Treasury securities in effect at the date of the grant of the stock options. The dividend yield is estimated based on our historic annual dividend payments and current expectations for the future. We applied the following weighted average assumptions to estimate the fair value of stock option grants made in the following periods, including the grants issued in connection with the Combination in fiscal 2015: 2016 2015 Expected term in years 7.0 3.9 Expected volatility 38.3 % 21.9 % Risk-free interest rate 1.6 % 2.4 % Dividend yield 4.5 % 1.3 % We did not grant any stock options in fiscal 2017. The expected term and the expected volatility in fiscal 2015 are lower than fiscal 2016 primarily as a result of the characteristics of the shares issued in connection with the Combination and our expectations for expected term and expected volatility following the Combination. The table below summarizes the changes in all stock options during the fiscal year ended September 30, 2017 : Stock Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in millions) Outstanding at September 30, 2016 8,065,816 $ 29.73 Exercised (2,074,828 ) 27.38 Expired (57,225 ) 32.61 Forfeited (67,636 ) 31.50 Outstanding at September 30, 2017 5,866,127 $ 30.51 4.6 $ 154.6 Exercisable at September 30, 2017 4,883,459 $ 29.94 4.0 $ 131.5 Vested and expected to vest at September 30, 2017 5,853,074 $ 30.50 4.6 $ 154.2 The weighted average grant date fair value for options granted during the fiscal years ended September 30, 2016 and 2015 was $8.06 and $28.78 per share, respectively. The aggregate intrinsic value of options exercised during the years ended September 30, 2017 , 2016 and 2015 was $54.3 million , $14.5 million and $25.1 million , respectively. As of September 30, 2017 , there was $2.4 million of total unrecognized compensation cost related to nonvested stock options; that cost is expected to be recognized over a weighted average remaining vesting period of 1.1 years. We amortize these costs on a straight-line basis over the explicit service period. As part of the Combination, we issued SARs to replace outstanding MWV SARs. The SARs were valued using the Black-Scholes option pricing model. We measure compensation expense related to the SAR awards at the end of each period. We do not expect to issue additional SARs. The table below summarizes the changes in all SARs during the fiscal year ended September 30, 2017 : SARs Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in millions) Outstanding at September 30, 2016 65,971 $ 26.07 Exercised (13,868 ) 28.43 Expired (1,087 ) 31.87 Outstanding at September 30, 2017 51,016 $ 25.30 2.8 $ 1.6 Exercisable at September 30, 2017 51,016 $ 25.30 2.8 $ 1.6 The aggregate intrinsic value of SARs exercised during the year ended September 30, 2017 and 2016 was $0.4 million and $0.2 million , respectively. Restricted Stock Restricted stock is typically granted annually to non-employee directors and certain of our employees. Our non-employee director awards generally vest over a period of up to one year and are treated as issued and carry dividend and voting rights until they vest. The vesting provisions for our employee awards may vary from grant to grant; however, vesting generally is contingent upon meeting various service and/or performance or market goals including, but not limited to, achievement of various financial targets including Cash Flow Per Share, Cash Flow to Equity Ratio and relative Total Shareholder Return (each as defined in the award documents). Subject to the level of performance attained, the target award for some of the grants may increase up to 200% of target or decrease to zero depending upon the terms of the individual grant. The employee grants generally vest in three years. Presently, other than circumstances such as death, disability and retirement, the grants generally include a provision requiring both a change of control and termination of employment to accelerate vesting. For certain employee grants, the grantee is entitled to receive dividend equivalent units, but will generally forfeit the restricted award and the dividend equivalents if the employee separates from us during the vesting period or if the predetermined goals are not accomplished. The table below summarizes the changes in unvested restricted stock during the fiscal year ended September 30, 2017 : Shares/Units Weighted Average Grant Date Fair Value Unvested at September 30, 2016 2,704,904 $ 40.89 Granted 1,605,113 53.79 Vested (1,112,909 ) 48.07 Forfeited (237,659 ) 39.69 Unvested at September 30, 2017 (1) 2,959,449 $ 45.28 (1) Target awards granted with a performance condition, net of subsequent forfeitures, may be increased up to 200% of the target or decreased to zero , subject to the level of performance attained. The awards are reflected in the table at the target award amount of 100% . Based on current facts and assumptions we are forecasting the performance of the grants to be attained at levels that would result in the issuance of approximately 1.4 million additional shares. However, it is possible that the performance attained may vary. There was approximately $83.5 million of unrecognized compensation cost related to all unvested restricted shares as of September 30, 2017 that will be recognized over a weighted average remaining vesting period of 1.6 years. The following table represents a summary of restricted stock shares granted in fiscal 2017 , 2016 and 2015 with terms defined in the applicable grant letters. The shares are not deemed to be issued and carry voting rights until the relevant conditions defined in the award documents have been met, unless otherwise noted. 2017 2016 2015 Shares of restricted stock granted to non-employee directors (1) 26,521 64,155 15,255 Shares of restricted stock granted to employees: Shares granted for attainment of a performance condition at an amount in excess of target (2) 340,319 447,261 801,810 Shares granted with a service condition and a Cash Flow Per Share performance condition at target (3) (4) 507,070 1,211,760 379,519 Shares granted with a service condition and a relative Total Shareholder Return market condition at target (3) 301,980 — — Shares granted with a service condition (5) 309,850 27,370 86,265 Shares granted with a service condition and a performance condition prorated upon the Combination (6) — — 64,323 Share of restricted stock assumed in purchase accounting: Shares granted with a service condition and a performance condition (7) (8) — — 650,685 Shares granted with a service condition (8) 119,373 — 327,005 Total restricted stock granted 1,605,113 1,750,546 2,324,862 (1) Non-employee director grants generally vest over a period of up to one year and are deemed issued on the grant date and have voting and dividend rights. (2) Shares granted in the table above include shares subsequently issued for the level of performance attained in excess of target. Shares issued in fiscal 2017 for the fiscal 2014 Cash Flow to Equity Ratio were at 176.6% of target. Shares issued in fiscal 2016 for the fiscal 2013 Cash Flow to Equity Ratio were at 200% of target. Shares issued in fiscal 2015 for the fiscal 2012 Cash Flow to Equity Ratio were at 200% of target. Shares issued in fiscal 2017, 2016 and 2015 also include shares accelerated for terminated employees primarily as a result of the Combination, which were achieved at between 146.5% and 200% of target. (3) These employee grants vest over approximately three years and have adjustable ranges from 0 - 200% of target subject to the level of performance attained in the respective award agreement. The employee grants with a relative Total Shareholder Return condition were valued using a Monte Carlo simulation, the terms of which are outlined below. (4) Shares granted in fiscal 2015 were reduced by 50,326 shares at target related to the rescission of shares granted to our CEO that were inadvertently granted in excess of plan limits. (5) These shares vest over approximately three to four years. (6) As a result of the Combination, certain target awards granted to employees in fiscal 2015 were prorated with the employee receiving approximately 16.6% of the target award in accordance with the terms in the award document prior to the application of the performance adjustment. The performance period applicable to each award ended upon consummation of the Combination, and the performance goals were determined in accordance with the applicable grant letter to be attained at 146.5% of target. (7) The performance period applicable to each award ended upon consummation of the Combination, and the performance goals were determined in accordance with the applicable grant letter to be attained at between 100% and 168% of target. (8) These shares vest over approximately one to three years. The employee grants with a relative Total Shareholder Return market condition were valued using a Monte Carlo simulation at $64.41 per share. The significant assumptions used in valuing these grants included: an expected term of 2.9 years , an expected volatility of 30.6% and a risk-free interest rate of 1.4% . We amortize these costs on a straight-line basis over the explicit service period. Expense is recognized on restricted stock grants on a straight-line basis over the explicit service period or for performance based grants over the explicit service period when we estimate that it is probable the performance conditions will be satisfied. Expense recognized on grants with a performance condition that affects how many shares are ultimately awarded is based on the number of shares expected to be awarded. The following table represents a summary of restricted stock vested in fiscal 2017 , 2016 and 2015 (in millions, except shares): 2017 2016 2015 Shares of restricted stock vested 1,112,909 1,589,761 1,725,435 Aggregate fair value of restricted stock vested $ 59.5 $ 57.5 $ 110.4 The shares vested in 2017 reflect the vesting of the fiscal 2014 grant, with a cash flow to equity ratio performance condition that vested at 176.6% of target, certain shares assumed upon the Combination with a performance and/or service condition, as well as other awards accelerated in connection with the Combination for certain former employees. The shares vested in 2016 reflect the vesting of the fiscal 2013 grant, with a cash flow to equity ratio performance condition that vested at maximum, certain shares assumed upon the Combination with a performance and/or service condition, as well as other awards accelerated in connection with the Combination for certain former employees. The shares vested in fiscal 2015 primarily reflect the vesting of the fiscal 2012 grant, with a cash flow to equity ratio performance condition that vested at maximum, as well as other awards accelerated in connection with the Combination for certain former employees. Employee Stock Purchase Plan Under the ESPP, shares of Common Stock are reserved for purchase by our qualifying employees. The ESPP allowed for the purchase of a total of approximately 2.5 million shares of Common Stock. During fiscal 2017 , 2016 and 2015 , including shares purchased under the then existing RockTenn Employee Stock Purchase Plan, employees purchased approximately 0.2 million , 0.1 million and 0.1 million shares, respectively, under the ESPP. We recognized $1.3 million , $0.4 million and $0.5 million of expense for fiscal 2017 , 2016 and 2015 , respectively, related to the 15% discount on the purchase price allowed to employees. As of September 30, 2017 , adjusted for the Separation, approximately 2.6 million shares of Common Stock remained available for purchase under the ESPP.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Sep. 30, 2017
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions We sell products to affiliated companies. Net sales to the affiliated companies for the fiscal years ended September 30, 2017 , 2016 and 2015 were approximately $423.6 million , $346.6 million and $342.8 million , respectively. Accounts receivable due from the affiliated companies at September 30, 2017 and 2016 was $65.1 million and $59.4 million , respectively, and was included in accounts receivable on our consolidated balance sheets.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Sep. 30, 2017
Commitments and Contingencies [Abstract]
Commitments and Contingencies	Commitments and Contingencies Capital Additions Estimated costs for future purchases of fixed assets that we are obligated to purchase as of September 30, 2017 , total approximately $155 million . Environmental and Other Matters Environmental compliance requirements are a significant factor affecting our business. We employ manufacturing processes that result in various discharges, emissions and wastes. These processes are subject to numerous federal, state, local and international environmental laws and regulations, as well as the requirements of environmental permits and similar authorizations issued by various governmental authorities. On January 31, 2013, the EPA published Boiler MACT. Boiler MACT required compliance by January 31, 2016 or by January 31, 2017 for those mills for which we obtained a prior compliance extension. All work required for our boilers to comply with the rule has been completed. On July 29, 2016, the U.S. Court of Appeals for the District of Columbia Circuit issued a ruling on the consolidated cases challenging Boiler MACT. The court vacated key portions of the rule, including emission limits for certain subcategories of solid fuel boilers, and remanded other issues to the EPA for further rulemaking. At this time, we cannot predict with certainty how this decision will impact our existing Boiler MACT strategies or whether we will incur additional costs to comply with any revised Boiler MACT standards. In addition to Boiler MACT, we are subject to a number of other federal, state, local and international environmental rules that may impact our business, including the National Ambient Air Quality Standards for nitrogen oxide, sulfur dioxide, fine particulate matter and ozone for facilities in the U.S. We are involved in various administrative proceedings relating to environmental matters that arise in the normal course of business, and may be involved in future matters. Although the ultimate outcome of such matters cannot be predicted with certainty and we cannot at this time estimate any reasonably possible losses based on available information, we do not believe that the currently expected outcome of any environmental proceedings and claims that are pending or threatened against us will have a material adverse effect on our results of operations, financial condition or cash flows. CERCLA and Other Remediation Costs We face potential liability under federal, state, local and international laws as a result of releases, or threatened releases, of hazardous substances into the environment from various sites owned and operated by third parties at which Company-generated wastes have allegedly been deposited. Generators of hazardous substances sent to off-site disposal locations at which environmental problems exist, as well as the owners of those sites and certain other classes of persons, are liable for response costs for the investigation and remediation of such sites under CERCLA and analogous laws. While joint and several liability is authorized under CERCLA, liability is typically shared with other PRPs, and costs are commonly allocated according to relative amounts of waste deposited and other factors. In addition, certain of our current or former locations are being investigated or remediated under various environmental laws, including CERCLA, and regulations. Based on information known to us and assumptions, we do not believe that the costs of these projects will have a material adverse effect on our results of operations, financial condition or cash flows. However, the discovery of contamination or the imposition of additional obligations at these or other sites in the future could result in additional costs. On January 26, 2009, Smurfit-Stone and certain of its subsidiaries filed a voluntary petition for relief under Chapter 11 of the U.S. Bankruptcy Code. Smurfit-Stone’s Canadian subsidiaries also filed to reorganize in Canada. We believe that matters relating to previously identified third party PRP sites and certain facilities formerly owned or operated by Smurfit-Stone have been or will be satisfied claims in the Smurfit-Stone bankruptcy proceedings. However, we may face additional liability for cleanup activity at sites that are not subject to the bankruptcy discharge, but are not currently identified. Some of these liabilities may be satisfied from existing bankruptcy reserves. We believe that we can assert claims for indemnification pursuant to existing rights we have under purchase and other agreements in connection with certain of our existing remediation sites. In addition, we believe that we have insurance coverage, subject to applicable deductibles/retentions, policy limits and other conditions, for certain environmental matters. However, there can be no assurance that we will be successful with respect to any claim regarding these insurance or indemnification rights, or that, if we are successful, any amounts paid pursuant to the insurance or indemnification rights will be sufficient to cover all our costs and expenses. We also cannot predict with certainty whether we will be required to perform remediation projects at other locations, and it is possible that our remediation requirements and costs could increase materially in the future and exceed current reserves. In addition, we cannot currently assess with certainty the impact that future changes in cleanup standards or federal, state or other environmental laws, regulations or enforcement practices will have on our results of operations, financial condition or cash flows. As of September 30, 2017 , we had $15.0 million reserved for environmental liabilities on an undiscounted basis, of which $9.6 million is included in other long-term liabilities and $5.4 million in other current liabilities, including amounts accrued in connection with environmental obligations relating to the manufacturing facilities that we have closed. We believe the liability for these matters was adequately reserved at September 30, 2017 . Climate Change Certain jurisdictions in which we have manufacturing facilities or other investments have taken actions to address climate change. The EPA has issued the Clean Air Act permitting regulations applicable to certain facilities that emit GHG. The EPA also has promulgated a rule requiring certain industrial facilities that emit 25,000 metric tons or more of carbon dioxide equivalent per year to file an annual report of their emissions. While we have facilities subject to existing GHG permitting and reporting requirements, the impact of these requirements has not been material to date. Additionally, the EPA has been working on a set of interrelated rulemakings aimed at cutting carbon emissions from power plants. On August 3, 2015, the EPA issued the Clean Power Plan. On the same day, the EPA issued a second rule setting standards of performance for new, modified and reconstructed electric utility generating units. While these rules do not apply directly to the power generation facilities at our mills, they have the potential to increase the cost of purchased electricity for our manufacturing operations and change the treatment of certain types of biomass that are currently considered carbon neutral. On February 9, 2016, the U.S. Supreme Court issued a stay halting implementation of the Clean Power Plan until the pending legal challenges to the rule are resolved. As directed by Executive Order, on April 4, 2017, the EPA issued a proposed rule announcing its intention to review the Clean Power Plan, and, if appropriate, initiate proceedings to suspend, revise or rescind it. A number of states subject to the Clean Power Plan have stopped working on their implementation strategies in response to the litigation and Executive Order; however, certain states where we operate manufacturing facilities have indicated their intention to continue their carbon reduction efforts. On October 16, 2017, the EPA issued a proposal rule that would repeal the Clean Power Plan. Due to ongoing litigation and other uncertainties regarding the Clean Power Plan, its impact on us cannot be quantified with certainty at this time. In addition to national efforts to regulate climate change, some U.S. states in which we have manufacturing operations are also taking measures to reduce GHG emissions, such as requiring GHG emissions reporting or developing regional cap-and trade programs. California has enacted a cap-and-trade program that took effect in 2012, and includes enforceable compliance obligations that began on January 1, 2013. In July 2017, California extended the cap-and-trade program to 2030. We do not have any manufacturing facilities that are subject to the cap-and-trade requirements in California; however, we are continuing to monitor the implementation of this program as well as proposed mandatory GHG reduction efforts in other states. Also, the Washington Department of Ecology has issued a final rule, known as the Clean Air Rule, which limits GHGs from facilities that have average annual carbon dioxide equivalent emissions equal to or exceeding 100,000 metric tons/year and proposes to begin GHG emissions reduction requirements for some regulated entities in 2017. Energy intensive and trade exposed facilities and transportation fuel importers, including our Tacoma, WA mill, are subject to regulation under this program. In September 2016, various groups filed lawsuits against the Washington Department of Ecology challenging the Clean Air Rule. We are carefully monitoring this litigation to assess its potential impact on our Tacoma operations. On May 16, 2017, the Governor of Virginia issued Executive Directive 11, directing the Secretary of Natural Resources to convene a work group to study and recommend methods to reduce carbon dioxide emissions from electric power facilities and grow the clean energy economy within existing state authority. We have been selected by the Virginia Department of Environmental Quality to participate in this work group. The Paris Agreement established a framework for reducing global GHG emissions. By signing the Paris Agreement, the U.S. made a non-binding commitment to reduce economy-wide GHG emissions by 26% to 28% below 2005 levels by 2025. Other countries in which we conduct business, including China, European Union member states and India, have set similar GHG reduction targets. The Paris Agreement became effective on November 4, 2016. Although a party to the agreement may not provide the required one-year notice of withdrawal until three years after the effective date, in June 2017, President Trump announced that the U.S. intended to withdraw from the Paris Agreement. The governors of New York, California and Washington subsequently announced their intent to form a “climate alliance” to coordinate a state response to climate change. At this time, it is not possible to determine how the Paris Agreement, or any potential U.S. commitments in lieu of those under the agreement, may impact U.S. industrial facilities, including our domestic operations. Several of our international facilities are located in countries that have already adopted GHG emissions trading schemes. For example, Quebec has become a member of the Western Climate Initiative, which is a collaboration among California and certain Canadian provinces that have joined together to create a cap-and-trade program to reduce GHG emissions. In 2009, Quebec adopted a target of reducing GHG emissions by 20% below 1990 levels by 2020 and 37.5% from 1990 levels by 2030. In 2011, Quebec issued a final regulation establishing a regional cap-and-trade program that required reductions in GHG emissions from covered emitters as of January 1, 2013. Our mill in Quebec is subject to these cap-and-trade requirements, although the direct impact of this regulation has not been material to date. Compliance with this program and other similar programs may require future expenditures to meet required GHG emission reduction requirements in future years. The regulation of climate change continues to develop in the areas of the world where we conduct business. We have systems in place for tracking the GHG emissions from our energy-intensive facilities, and we carefully monitor developments in climate change laws, regulations and policies to assess the potential impact of such developments on our results of operations, financial condition, cash flows and disclosure obligations. Litigation The complaint in the Antitrust Litigation seeks treble damages and costs, including attorney’s fees. In March 2015, the court granted the plaintiffs’ motion for class certification. On January 9, 2017, the defendants filed individual and joint Motions for Summary Judgment in the District Court. On August 3, 2017, the District Court granted our Motion for Summary Judgment with respect to all claims against us. The plaintiffs have filed a notice of appeal. As with numerous other large industrial companies, we have been named a defendant in asbestos-related personal injury litigation. Typically, these suits also name many other corporate defendants. To date, the costs resulting from the litigation, including settlement costs, have not been significant. As of September 30, 2017 , there were approximately 725 lawsuits. We believe that we have substantial insurance coverage, subject to applicable deductibles and policy limits, with respect to asbestos claims. We have valid defenses to these asbestos-related personal injury claims and intend to continue to defend them vigorously. Should the volume of litigation grow substantially, it is possible that we could incur significant costs resolving these cases. We do not expect the resolution of pending litigation and proceedings to have a material adverse effect on our consolidated financial condition or liquidity. In any given period or periods, however, it is possible such proceedings or matters could have a material adverse effect on our results of operations. We are a defendant in a number of other lawsuits and claims arising out of the conduct of our business. While the ultimate results of such suits or other proceedings against us cannot be predicted with certainty, we believe the resolution of these other matters will not have a material adverse effect on our results of operations, consolidated financial condition or cash flows. Guarantees We make certain guarantees in the course of conducting our operations, for compliance with certain laws and regulations, or in connection with certain business dispositions. The guarantees include items such as funding of net losses in proportion to our ownership share of certain joint ventures, debt guarantees related to certain unconsolidated entities acquired in acquisitions, indemnifications of lessors in certain facilities and equipment operating leases for items such as additional taxes being assessed due to a change in tax law, and, certain other agreements. We estimate the exposure for these matters could be approximately $50 million . As of September 30, 2017 , we have recorded $11.9 million for the estimated fair value of these guarantees. We are unable to estimate our maximum exposure under operating leases because it is dependent on potential changes in the tax law, however, we believe our exposure related to guarantees would not have a material impact on our results of operations, financial condition or cash flows.

Special Purpose Entities (Notes

Special Purpose Entities (Notes)	12 Months Ended
	Sep. 30, 2017
Debt Instrument [Line Items]
Special Purpose Entities [Text Block]	Special Purpose Entities Pursuant to a sale of certain large-tract forestlands in 2007, a special purpose entity MWV Timber Notes Holding, LLC received, and WestRock assumed upon the Combination, an installment note receivable in the amount of $398.0 million . The Timber Note does not require any principal payments until its maturity in October 2027 and bears interest at a rate approximating LIBOR. In addition, the Timber Note is supported by a bank-issued irrevocable letter of credit obtained by the buyer of the forestlands. The Timber Note is not subject to prepayment in whole or in part prior to maturity. The bank’s credit rating as of November 2017 was investment grade. Using the Timber Note as collateral, MWV TN received $338.3 million in proceeds under a secured financing agreement with a bank. Under the terms of the agreement, the liability from this transaction is non-recourse to the Company and is payable from the Timber Note proceeds upon its maturity in October 2027. As a result, the Timber Note is not available to satisfy any obligations of WestRock. MWV TN can elect to prepay at any time the liability in whole or in part, however, given that the Timber Note is not prepayable, MWV TN expects to only repay the liability at maturity from the Timber Note proceeds. The Timber Note and the secured financing liability were fair valued on the opening balance sheet in connection with the Combination. As of September 30, 2017 , the Timber Note was $363.0 million and is included within restricted assets held by special purpose entities on the consolidated balance sheet and the secured financing liability was $321.7 million and is included within non-recourse liabilities held by special purpose entities on the consolidated balance sheet. Pursuant to the sale of MWV’s remaining U.S. forestlands, which occurred on December 6, 2013, another special purpose entity MWV Timber Notes Holding Company II, LLC received, and WestRock assumed upon the Combination, an installment note receivable in the amount of $860.0 million . The Installment Note does not require any principal payments until its maturity in December 2023 and bears interest at a fixed rate of 5.207% . However, at any time during a 180-day period following receipt by the borrower of notice from us that we intend to withhold our consent to any amendment or waiver of this Installment Note that was requested by the borrower and approved by any eligible assignees, the borrower may prepay the Installment Note in whole but not in part for cash at 100% of the principal, plus accrued but unpaid interest, breakage, or other similar amount if any. As of September 30, 2017, no event had occurred that would allow for the prepayment of the Installment Note. We monitor the credit quality of the borrower and receive quarterly compliance certificates. The borrower’s credit rating as of November 2017 was investment grade. Using the Installment Note as collateral, MWV TN II received $774.0 million in proceeds under a secured financing agreement with a bank. Under the terms of the agreement, the liability from this transaction is non-recourse to WestRock and is payable from the Installment Note proceeds upon its maturity in December 2023. As a result, the Installment Note is not available to satisfy any obligations of WestRock. MWV TN II can elect to prepay, at any time, the liability in whole or in part, with sufficient notice, but would avail itself of this provision only in the event the Installment Note was prepaid in whole or in part. The secured financing agreement however requires a mandatory repayment, up to the amount of cash received, if the Installment Note is prepaid in whole or in part. The Installment Note and the secured financing liability were fair valued on the opening balance sheet in connection with the Combination. As of September 30, 2017 , the Installment Note was $924.4 million and is included within restricted assets held by special purpose entities on the consolidated balance sheet and the secured financing liability was $840.2 million and is included within non-recourse liabilities held by special purpose entities on the consolidated balance sheet.

Segment Information

Segment Information	12 Months Ended
	Sep. 30, 2017
Segment Information [Abstract]
Segment Information	Segment Information Subsequent to the Separation, we report our financial results of operations in the following three reportable segments: Corrugated Packaging, which consists of our containerboard mill and corrugated packaging operations, as well as our recycling operations; Consumer Packaging, which consists of consumer mills, folding carton, beverage, merchandising displays, home, health and beauty dispensing (prior to the HH&B Sale), and partition operations; and Land and Development, which sells real estate primarily in the Charleston, SC region. Certain income and expenses are not allocated to our segments and, thus, the information that management uses to make operating decisions and assess performance does not reflect such amounts. Items not allocated are reported as non-allocated expenses or in other line items in the table below after segment income. Some of our operations included in the segments are located in locations such as Canada, Mexico, South America, Europe, Asia and Australia. The table below reflects financial data of our foreign operations for each of the past three fiscal years (in millions, except percentages): Years Ended September 30, 2017 2016 2015 Foreign net sales to unaffiliated customers $ 2,621.2 $ 2,426.6 $ 1,506.5 Foreign segment income $ 260.1 $ 226.1 $ 171.6 Foreign long-lived assets $ 1,558.3 $ 1,341.5 $ 1,228.0 Foreign operations as a percent of consolidated operations: Foreign net sales to unaffiliated customers 17.6 % 17.1 % 13.5 % Foreign segment income 21.8 % 18.4 % 16.0 % Foreign long-lived assets 17.1 % 14.4 % 13.4 % We evaluate performance and allocate resources based, in part, on profit from operations before income taxes, interest and other items. The accounting policies of the reportable segments are the same as those described in “ Note 1. Description of Business and Summary of Significant Accounting Policies ”. We account for intersegment sales at prices that approximate market prices. For segment reporting purposes, we include our equity in income of unconsolidated entities in segment income, as well as our investments in unconsolidated entities in segment identifiable assets. Equity in income of unconsolidated entities is not material and we disclose our investments in unconsolidated entities below. Certain income and expenses are not allocated to our segments and, thus, the information that management uses to make operating decisions and assess performance does not reflect such amounts. Items not allocated are reported as non-allocated expenses or in other line items in the table below after segment income. The following table shows selected operating data for our segments (in millions): Years Ended September 30, 2017 2016 2015 Net sales (aggregate): Corrugated Packaging $ 8,408.3 $ 7,868.5 $ 7,516.9 Consumer Packaging 6,452.5 6,388.1 3,740.1 Land and Development 243.8 119.8 45.0 Total $ 15,104.6 $ 14,376.4 $ 11,302.0 Less net sales (intersegment): Corrugated Packaging $ 155.8 $ 136.2 $ 130.6 Consumer Packaging 89.1 68.4 46.6 Total $ 244.9 $ 204.6 $ 177.2 Net sales (unaffiliated customers): Corrugated Packaging $ 8,252.5 $ 7,732.3 $ 7,386.3 Consumer Packaging 6,363.4 6,319.7 3,693.5 Land and Development 243.8 119.8 45.0 Total $ 14,859.7 $ 14,171.8 $ 11,124.8 Segment income: Corrugated Packaging $ 753.9 $ 739.9 $ 806.7 Consumer Packaging 425.8 481.7 267.0 Land and Development 13.8 4.6 (3.4 ) Segment income 1,193.5 1,226.2 1,070.3 Pension risk transfer expense — (370.7 ) — Pension lump sum settlement and retiree medical curtailment, net (32.6 ) — (11.5 ) Land and Development impairment (46.7 ) — — Restructuring and other costs, net (196.7 ) (366.4 ) (140.8 ) Non-allocated expenses (43.5 ) (49.1 ) (58.4 ) Interest expense (277.7 ) (256.7 ) (132.5 ) Gain (loss) on extinguishment of debt 1.8 2.7 (2.6 ) Interest income and other income (expense), net 66.7 58.6 9.7 Gain on sale of HH&B 192.8 — — Income from continuing operations before income taxes $ 857.6 $ 244.6 $ 734.2 Segment income in fiscal 2017 , 2016 and 2015 was reduced by $26.5 million , $8.1 million and $64.7 million , respectively, of expense for inventory stepped-up in purchase accounting, net of related LIFO impact. Corrugated Packaging segment income and Consumer Packaging segment income in fiscal 2017 were reduced by $1.4 million and $25.1 million , respectively. The Corrugated Packaging segment income and Consumer Packaging segment income in fiscal 2016 were reduced by $3.4 million and $4.7 million , respectively. Corrugated Packaging segment income and Consumer Packaging segment income in fiscal 2015 were reduced by $2.2 million and $62.5 million , respectively. The following table shows selected operating data for our segments (in millions): Years Ended September 30, 2017 2016 2015 Identifiable assets: Corrugated Packaging $ 10,537.7 $ 10,046.0 $ 9,467.3 Consumer Packaging 11,877.8 10,122.5 10,175.7 Land and Development 89.8 460.6 545.5 Assets of discontinued operations — — 2,618.5 Assets held for sale 173.6 52.3 10.2 Corporate 2,410.1 2,356.8 2,555.2 Total $ 25,089.0 $ 23,038.2 $ 25,372.4 Goodwill: Corrugated Packaging $ 1,865.7 $ 1,722.5 $ 1,667.5 Consumer Packaging 3,662.6 3,055.6 2,979.6 Total $ 5,528.3 $ 4,778.1 $ 4,647.1 Depreciation and amortization: Corrugated Packaging $ 597.9 $ 576.2 $ 496.6 Consumer Packaging 508.2 498.9 201.8 Land and Development 0.7 1.4 0.2 Discontinued operations — 57.2 22.0 Corporate 9.8 12.8 20.2 Total $ 1,116.6 $ 1,146.5 $ 740.8 Capital expenditures: Corrugated Packaging $ 492.1 $ 490.1 $ 378.4 Consumer Packaging 265.8 244.9 166.1 Discontinued operations — 45.2 28.6 Corporate 20.7 16.5 12.4 Total $ 778.6 $ 796.7 $ 585.5 Investment in unconsolidated entities: Corrugated Packaging $ 321.1 $ 281.2 $ 7.9 Consumer Packaging 24.7 22.2 21.3 Land and Development 14.4 28.6 31.0 Corporate 0.4 (3.1 ) — Total $ 360.6 $ 328.9 $ 60.2 The increase in the Corrugated Packaging segment’s investment in unconsolidated entities in fiscal 2016 was primarily related to the Grupo Gondi investment. The Corporate investment in unconsolidated entities in fiscal 2016 primarily represented an entity that had losses that were guaranteed equally by the partners; this subsidiary has since been sold. The investment in Grupo Gondi that is included in the Corrugated Packaging segment’s investment in unconsolidated entities in fiscal 2017 and 2016 exceeds our proportionate share of the underlying equity in net assets by approximately $76.2 million and $65.3 million , respectively. Approximately $59.2 million and $56.2 million remains amortizable to expense in equity in income of unconsolidated entities over the estimated life of the underlying assets ranging from 10 to 15 years beginning with our investment in fiscal 2016. In fiscal 2017, our equity participation in the Grupo Gondi joint venture increased due to the joint venture entity’s stock redemption from a minority partner. As a result, our equity participation in the joint venture increased to approximately 27.0% . See “ Note 23. Subsequent Events (Unaudited) — Grupo Gondi Investment ” for recent developments. The changes in the carrying amount of goodwill for the fiscal years ended September 30, 2017 , 2016 and 2015 are as follows (in millions): Corrugated Packaging Consumer Packaging Total Balance as of October 1, 2014 Goodwill $ 1,525.4 $ 443.8 $ 1,969.2 Accumulated impairment losses — (42.8 ) (42.8 ) 1,525.4 401.0 1,926.4 Goodwill acquired 183.3 2,586.5 2,769.8 Purchase price allocation adjustments 2.4 (1.1 ) 1.3 Translation adjustment (43.6 ) (6.8 ) (50.4 ) Balance as of September 30, 2015 Goodwill 1,667.5 3,022.4 4,689.9 Accumulated impairment losses — (42.8 ) (42.8 ) 1,667.5 2,979.6 4,647.1 Goodwill acquired 52.4 8.0 60.4 Goodwill disposed of (24.0 ) — (24.0 ) Purchase price allocation adjustments (4.9 ) 67.6 62.7 Translation adjustment 31.5 0.4 31.9 Balance as of September 30, 2016 Goodwill 1,722.5 3,098.4 4,820.9 Accumulated impairment losses — (42.8 ) (42.8 ) 1,722.5 3,055.6 4,778.1 Goodwill acquired 137.6 907.8 1,045.4 Goodwill disposed of — (329.6 ) (329.6 ) Purchase price allocation adjustments (1.2 ) 9.3 8.1 Translation adjustment 6.8 19.5 26.3 Balance as of September 30, 2017 Goodwill 1,865.7 3,705.4 5,571.1 Accumulated impairment losses — (42.8 ) (42.8 ) $ 1,865.7 $ 3,662.6 $ 5,528.3 The goodwill acquired in fiscal 2017 related to the MPS Acquisition and the Hannapak Acquisition in the Consumer Packaging segment and the U.S. Corrugated Acquisition, the Island Container Acquisition and the Star Pizza Acquisition in the Corrugated Packaging segment. The goodwill disposed of in the Consumer Packaging segment in fiscal 2017 was primarily related to the HH&B Sale. The goodwill acquired in fiscal 2016 related to the SP Fiber Acquisition and the Packaging Acquisition in the Corrugated Packaging and Consumer Packaging segments, respectively. The goodwill disposed of in the Corrugated Packaging segment in fiscal 2016 relates to the disposal of a portion of the reporting unit in connection with the investment in the Grupo Gondi unconsolidated joint venture. The goodwill acquired in fiscal 2015 primarily relates to the Combination. See “ Note 6. Merger, Acquisitions and Investment ”.

Financial Results by Quarter (U

Financial Results by Quarter (Unaudited)	12 Months Ended
	Sep. 30, 2017
Financial Results by Quarter (Unaudited) [Abstract]
Financial Results by Quarter	Financial Results by Quarter (Unaudited) Fiscal 2017 First Quarter Second Quarter Third Quarter Fourth Quarter (In millions, except per share data) Net sales $ 3,447.2 $ 3,656.3 $ 3,695.6 $ 4,060.6 Gross profit $ 591.3 $ 675.4 $ 695.5 $ 778.0 Pension lump sum settlement and retiree medical curtailment, net $ — $ 28.7 $ — $ 3.9 Land and Development impairment $ — $ 42.7 $ — $ 4.0 Restructuring and other costs, net $ 81.0 $ 18.3 $ 59.4 $ 38.0 (Loss) gain on extinguishment of debt $ — $ (0.1 ) $ 2.0 $ (0.1 ) Gain on sale of HH&B $ — $ — $ 190.6 $ 2.2 Consolidated net income $ 78.5 $ 98.2 $ 326.6 $ 195.3 Net income attributable to common stockholders $ 80.9 $ 103.1 $ 328.1 $ 196.1 Basic earnings per share attributable to common stockholders $ 0.32 $ 0.40 $ 1.29 $ 0.77 Diluted earnings per share attributable to common stockholders $ 0.32 $ 0.40 $ 1.29 $ 0.76 Fiscal 2016 First Quarter Second Quarter Third Quarter Fourth Quarter (In millions, except per share data) Net sales $ 3,470.9 $ 3,492.7 $ 3,596.5 $ 3,611.7 Gross profit $ 654.7 $ 657.3 $ 727.3 $ 719.3 Pension risk transfer expense $ — $ — $ — $ 370.7 Restructuring and other costs, net $ 162.8 $ 111.1 $ 43.1 $ 49.4 Gain on extinguishment of debt $ — $ — $ — $ 2.7 Income (loss) from continuing operations $ 30.4 $ 58.4 $ 152.4 $ (86.4 ) (Loss) income from discontinued operations, net of tax $ (482.1 ) $ 1.4 $ (58.7 ) $ (5.3 ) Consolidated net (loss) income $ (451.7 ) $ 59.8 $ 93.7 $ (91.7 ) Net (loss) income attributable to common stockholders $ (453.5 ) $ 56.9 $ 92.3 $ (92.0 ) Basic earnings (loss) per share from continuing operations $ 0.12 $ 0.22 $ 0.60 $ (0.34 ) Diluted earnings (loss) per share from continuing operations $ 0.12 $ 0.22 $ 0.59 $ (0.34 ) Basic (loss) earnings per share attributable to common stockholders $ (1.76 ) $ 0.22 $ 0.37 $ (0.37 ) Diluted (loss) earnings per share attributable to common stockholders $ (1.73 ) $ 0.22 $ 0.36 $ (0.37 ) We computed the interim earnings per common and common equivalent share amounts as if each quarter was a discrete period. As a result, the sum of the basic and diluted earnings per share by quarter will not necessarily total the annual basic and diluted earnings per share. Consolidated net income in the first quarter of fiscal 2017 financial results by quarter (unaudited) table was increased due to a $23.8 million tax benefit related to the reduction of a state deferred tax liability as a result of an internal U.S. legal entity restructuring that will simplify future operating activities within the U.S. Basic and diluted earnings per share attributable to common stockholders were each increased by approximately $0.09 per share. Consolidated net income in the second quarter of fiscal 2017 financial results by quarter (unaudited) table was decreased due to a non-cash charge of $28.7 million recorded on the line item “Pension lump sum settlement” on our Consolidated Statements of Operations related to our year to date lump sum payments to certain beneficiaries of the Plan, together with several one-time severance benefit payments out of the Plan, triggered pension settlement accounting. For additional information see “ Note 15. Retirement Plans ” . Additionally, consolidated net income in the second quarter of fiscal 2017 financial results by quarter (unaudited) table was decreased due to a non-cash charge of $42.7 million , or $36.3 million net of $6.4 million of noncontrolling interest, recorded on the line item “Land and development impairment” on our Consolidated Statements of Operations due to the accelerated monetization strategy in our Land and Development segment. The impairment was recorded to write-down the carrying value on projects where the projected sales proceeds were less than the carrying value. Basic and diluted earnings per share attributable to common stockholders were each decreased by approximately $0.16 per share for these items. Consolidated net income in the third quarter of fiscal 2017 financial results by quarter (unaudited) table was increased due to a pre-tax gain on sale of HH&B of $190.6 million . Basic and diluted earnings per share from continuing operations and basic and diluted earnings per share attributable to common stockholders were each increased by approximately $0.76 and $0.75 per share, respectively. See “Note 8. Assets Held For Sale” for additional information. (Loss) income from discontinued operations in the first quarter of fiscal 2016 financial results by quarter (unaudited) table includes a pre-tax non-cash goodwill impairment charge of $478.3 million as a result of our evaluation of whether events or changes in circumstances had occurred that would indicate whether it was more likely than not that the goodwill of our then-owned Specialty Chemicals reporting unit was impaired. No tax benefit was recorded for the goodwill impairment. See “ Note 7. Discontinued Operations ” for additional information. Basic and diluted earnings per share attributable to common stockholders were decreased by approximately $1.86 and $1.83 per share, respectively. (Loss) income from discontinued operations in the third quarter of fiscal 2016 financial results by quarter (unaudited) table includes a $101.1 million pre-tax non-cash impairment of our Specialty Chemicals customer relationships intangible that was evaluated at the time of the Separation. Basic and diluted earnings per share attributable to common stockholders were each decreased by approximately $0.27 per share. See “ Note 7. Discontinued Operations ” for additional information. Income from continuing operations in the fourth quarter of fiscal 2016 financial results by quarter (unaudited) table was decreased due to a non-cash charge of $370.7 million recorded on the line item “Pension risk transfer expense” on our Consolidated Statements of Operations as we settled $2.5 billion in pension obligations of the Plan. Basic and diluted earnings per share from continuing operations and basic and diluted earnings per share attributable to common stockholders were each decreased by approximately $0.91 per share. See “ Note 15. Retirement Plans ” for additional information.

Subsequent Event

Subsequent Event	12 Months Ended
	Sep. 30, 2017
Subsequent Event [Line Items]
Subsequent Events [Text Block]	Subsequent Events (Unaudited) Grupo Gondi Investment On October 20, 2017, we increased our ownership interest in the Grupo Gondi joint venture to approximately 32.3% through a $108 million capital contribution, which followed a redemption of a minority partner in April 2017. The capital contribution will be used to support the joint venture’s capital expansion plans, including related to a greenfield containerboard mill and several converting plants. Each partner continues to hold future put and call rights with respect to its respective ownership interest in the joint venture. Commercial Paper Program On October 31, 2017, we established an unsecured commercial paper program, pursuant to which we may issue short-term, unsecured commercial paper notes in an aggregate principal amount at any time not to exceed $1.0 billion . Amounts available under the program may be borrowed, repaid and re-borrowed from time to time. The net proceeds of issuances of the notes under the program are expected to be used for general corporate purposes. Capital Investment in Florence, South Carolina Mill On November 16, 2017, we announced our intention to invest approximately $410 million over two years in connection with installing a 330” kraft linerboard machine and related infrastructure that will replace three older, narrow-width paper machines at our kraft linerboard mill located in Florence, South Carolina. In addition, we expect to invest approximately $60 million over the next five years to support the new machine and other projects. We expect the new machine to become operational in the first half of calendar 2020 and to produce 710,000 tons of kraft linerboard annually. New Revolving Credit Facility On October 31, 2017, we entered into a credit agreement with Wells Fargo Bank, National Association, as administrative agent, providing for a 364-day senior unsecured revolving credit facility in an aggregate committed principal amount of $450.0 million . The proceeds of the credit facility may be used for working capital and for other general corporate purposes. The credit facility is unsecured and is guaranteed by WestRock RKT Company and WestRock MWV, LLC. At our option, loans issued under the credit facility will bear interest at either LIBOR or an alternate base rate, in each case plus an applicable interest rate margin. Other Activity On October 31, 2017, we borrowed $485.0 million under our Receivables Facility and prepaid $485.0 million outstanding under our term loan. There are no further amortization payments due under the term loan facility until its maturity. See “ Note 11. Debt ” for additional information about these facilities.

Description of Business and S34

Description of Business and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2017
Consolidation, Policy [Policy Text Block]	Consolidation The consolidated financial statements include our accounts and the accounts of our partially-owned consolidated subsidiaries. Equity investments in which we exercise significant influence but do not control and are not the primary beneficiary are accounted for using the equity method. Investments in which we are not able to exercise significant influence over the investee are accounted for under the cost method. Our equity and cost method investments are not significant either individually or in the aggregate. We have eliminated all significant intercompany accounts and transactions. See “ Note 21. Segment Information ” for our equity method investments.
Use of Estimates, Policy [Policy Text Block]	Use of Estimates Preparing consolidated financial statements in conformity with GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates, and the differences could be material. The most significant accounting estimates inherent in the preparation of our consolidated financial statements include estimates to evaluate the recoverability of goodwill, intangibles and property, plant and equipment, to determine the useful lives of assets that are amortized or depreciated, and to measure income taxes, self-insured obligations, restructuring activities and allocate the purchase price of an acquired business to the fair value of acquired assets and liabilities. In addition, significant estimates form the basis for our reserves with respect to collectibility of accounts receivable, inventory valuations, pension benefits, deferred tax asset valuation allowances and certain benefits provided to current and retired employees. Various assumptions and other factors underlie the determination of these significant estimates. The process of determining significant estimates is fact specific and takes into account factors such as historical experience, current and expected economic conditions, product mix, and in some cases, actuarial techniques. We regularly evaluate these significant factors and make adjustments where facts and circumstances dictate.
Revenue Recognition, Policy [Policy Text Block]	Revenue Recognition We recognize revenue when there is persuasive evidence that an arrangement exists, delivery has occurred or services have been rendered, our price to the buyer is fixed or determinable and collectibility is reasonably assured. Delivery is not considered to have occurred until the customer takes title and assumes the risks and rewards of ownership. The timing of revenue recognition is dependent on the location of title transfer which is normally either on the exit from our plants (i.e., shipping point) or on arrival at customers’ plants (i.e., destination point). We do not recognize revenue from transactions where we bill customers, but retain custody and title to these products until the date custody and title transfer. We do not have any significant multiple deliverable revenue arrangements. We net, against our gross sales, provisions for discounts, returns, allowances, customer rebates and other adjustments. We account for such provisions during the same period in which we record the related revenues. We include in net sales any amounts related to shipping and handling that are billed to a customer.
Shipping and Handling Cost, Policy [Policy Text Block]	Shipping and Handling Costs We classify shipping and handling costs as a component of cost of goods sold.
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash Equivalents We consider all highly liquid investments that mature three months or less from the date of purchase to be cash equivalents. The carrying amounts we report in the consolidated balance sheets for cash and cash equivalents approximate fair market values. We place our cash and cash equivalents with large credit worthy banks, which limits the amount of our credit exposure.
Receivables, Policy [Policy Text Block]	Accounts Receivable and Allowances We perform periodic evaluations of our customers’ financial condition and generally do not require collateral. The weighted average of our receivables collection is within 30 to 60 days. We sell certain receivables under our A/R Sales Agreement. We serve a diverse customer base primarily in North America, South America, Europe, Asia and Australia, and, therefore, have limited exposure from credit loss to any particular customer or industry segment. We state accounts receivable at the amount owed by the customer, net of an allowance for estimated uncollectible accounts, returns and allowances, cash discounts and other adjustments. We do not discount accounts receivable because we generally collect accounts receivable over a relatively short time. We account for sales and other taxes that are imposed on and concurrent with individual revenue-producing transactions between a customer and us on a net basis which excludes the taxes from our net sales. We estimate our allowance for doubtful accounts based on our historical experience, current economic conditions and the credit worthiness of our customers. We charge off receivables when they are determined to be no longer collectible. In fiscal 2017 , 2016 and 2015 our bad debt expense was not significant. The following table represents a summary of the changes in the reserve for allowance for doubtful accounts, returns and allowances and cash discounts for fiscal 2017 , 2016 and 2015 (in millions): 2017 2016 2015 Balance at beginning of fiscal year $ 36.5 $ 29.5 $ 25.1 Reduction in sales and charges to costs and expenses 215.6 200.8 166.6 Deductions (206.3 ) (193.8 ) (162.2 ) Balance at end of fiscal year $ 45.8 $ 36.5 $ 29.5
Inventory, Policy [Policy Text Block]	Inventories We value substantially all U.S. inventories at the lower of cost or market, with cost determined on the LIFO basis. We value all other inventories at the lower of cost or market, with cost determined using methods that approximate cost computed on a FIFO basis. These other inventories represent primarily foreign inventories, spare parts inventories and certain inventoried supplies and aggregate to approximately 32% and 35% of FIFO cost of all inventory at September 30, 2017 and 2016 , respectively. Prior to the application of the LIFO method, our U.S. operating divisions use a variety of methods to estimate the FIFO cost of their finished goods inventories. Such methods include standard costs, or average costs computed by dividing the actual cost of goods manufactured by the tons produced and multiplying this amount by the tons of inventory on hand. Lastly, certain operations calculate a ratio, on a plant by plant basis, the numerator of which is the cost of goods sold and the denominator is net sales. This ratio is applied to the estimated sales value of the finished goods inventory. Variances and other unusual items are analyzed to determine whether it is appropriate to include those items in the value of inventory. Examples of variances and unusual items that are considered to be current period charges include, but are not limited to, abnormal production levels, freight, handling costs, and wasted materials (spoilage). Cost includes raw materials and supplies, direct labor, indirect labor related to the manufacturing process and depreciation and other factory overheads. Our inventoried spare parts are measured at average cost.
Property, Plant and Equipment, Policy [Policy Text Block]	Property, Plant and Equipment We state property, plant and equipment at cost. Cost includes major expenditures for improvements and replacements that extend useful lives, increase capacity, increase revenues or reduce costs. During fiscal 2017 , 2016 and 2015 , we capitalized interest of approximately $7.0 million , $7.6 million and $4.0 million , respectively. For financial reporting purposes, we provide depreciation and amortization primarily on a straight-line method generally over the estimated useful lives of the assets as follows: Buildings and building improvements 15-40 years Machinery and equipment 3-25 years Transportation equipment 3-8 years Generally, our machinery and equipment have estimated useful lives between 3 and 25 years; however, select portions of machinery and equipment primarily at our mills have estimated useful lives up to 44 years. Greater than 90% of the cost of our mill assets have lives of 25 years or less. Leasehold improvements are depreciated over the shorter of the asset life or the lease term, generally between 3 and 10 years.
Goodwill and Intangible Assets, Policy [Policy Text Block]	Goodwill and Long-Lived Assets We review the carrying value of our goodwill annually at the beginning of the fourth quarter of each fiscal year, or more often if events or changes in circumstances indicate that the carrying amount may exceed fair value as set forth in ASC 350, “Intangibles — Goodwill and Other.” See “ Note 7. Discontinued Operations ” for information on the first quarter of fiscal 2016 goodwill impairment test and resulting charge. We test goodwill for impairment at the reporting unit level, which is an operating segment or one level below an operating segment, referred to as a component. A component of an operating segment is a reporting unit if the component constitutes a business for which discrete financial information is available and segment management regularly reviews the operating results of that component. However, two or more components of an operating segment are aggregated and deemed a single reporting unit if the components have similar economic characteristics. The amount of goodwill acquired in a business combination that is assigned to one or more reporting units as of the acquisition date is the excess of the purchase price of the acquired businesses (or portion thereof) included in the reporting unit, over the fair value assigned to the individual assets acquired or liabilities assumed. Goodwill is assigned to the reporting unit(s) expected to benefit from the synergies of the combination even though other assets or liabilities of the acquired entity may not be assigned to that reporting unit. We determine recoverability by comparing the estimated fair value of the reporting unit to which the goodwill applies to the carrying value, including goodwill, of that reporting unit using a discounted cash flow model. Prior to the adoption of ASU 2017-04, “ Simplifying the Test for Goodwill Impairment ”, the goodwill impairment model is a two-step process. We have not yet adopted the ASU. An amendment to ASC 350 became effective December 2011 that allows a qualitative assessment, prior to step one, to determine whether it is more likely than not that the fair value of a reporting unit exceeds its carrying amount. We did not attempt a qualitative assessment and moved directly to step one. In step one, we utilize the present value of expected net cash flows to determine the estimated fair value of our reporting units. This present value model requires management to estimate future net cash flows, the timing of these cash flows, and a discount rate (based on a weighted average cost of capital), which represents the time value of money and the inherent risk and uncertainty of the future cash flows. Factors that management must estimate when performing this step in the process include, among other items, sales volume, prices, inflation, discount rates, exchange rates, tax rates, anticipated synergies and productivity improvements resulting from acquisitions, capital expenditures and continuous improvement projects. The assumptions we use to estimate future cash flows are consistent with the assumptions that the reporting units use for internal planning purposes, updated to reflect current expectations. If we determine that the estimated fair value of the reporting unit exceeds its carrying amount, goodwill of the reporting unit is not impaired. If we determine that the carrying amount of the reporting unit exceeds its estimated fair value, we would complete step two of the impairment analysis. Step two involves determining the implied fair value of the reporting unit’s goodwill and comparing it to the carrying amount of that goodwill. If the carrying amount of the reporting unit’s goodwill exceeds the implied fair value of that goodwill, we recognize an impairment loss in an amount equal to that excess. During the fourth quarter of fiscal 2017 , of those reporting units that have goodwill, our Consumer Packaging and Brazil Corrugated reporting units had a fair value which exceeded their carrying value by a little more than 10%, due primarily to the Combination and the MPS Acquisition and the corresponding fair value accounting. If we had concluded that it was appropriate to increase the discount rate we used by 100 basis point to estimate the fair value of each reporting unit that has goodwill, the fair value for each of our reporting units would have continued to exceed its carrying value except for the Consumer Packaging and Brazil Corrugated reporting units. No events have occurred since the latest annual goodwill impairment assessment that would necessitate an interim goodwill impairment assessment. We follow the provisions included in ASC 360, “Property, Plant and Equipment” in determining whether the carrying value of any of our long-lived assets, including amortizing intangibles other than goodwill, is impaired. The ASC 360 test is a three-step test for assets that are “held and used” as that term is defined by ASC 360. We determine whether indicators of impairment are present. We review long-lived assets for impairment when events or changes in circumstances indicate that the carrying amount of the long-lived asset might not be recoverable. If we determine that indicators of impairment are present, we determine whether the estimated undiscounted cash flows for the potentially impaired assets are less than the carrying value. This requires management to estimate future net cash flows through operations over the remaining useful life of the asset and its ultimate disposition. The assumptions we use to estimate future cash flows are consistent with the assumptions we use for internal planning purposes, updated to reflect current expectations. If our estimated undiscounted cash flows do not exceed the carrying value, we estimate the fair value of the asset and record an impairment charge if the carrying value is greater than the fair value of the asset. We estimate fair value using discounted cash flows, observable prices for similar assets, or other valuation techniques. We record assets classified as “held for sale” at the lower of their carrying value or estimated fair value less anticipated costs to sell. Included in our long-lived assets are certain identifiable intangible assets. These intangible assets are amortized based on the approximate pattern in which the economic benefits are consumed or straight-line if the pattern was not reliably determinable. Estimated useful lives range from 1 to 40 years and have a weighted average life of approximately 16.6 years. Our judgments regarding the existence of impairment indicators are based on legal factors, market conditions and operational performance. Future events could cause us to conclude that impairment indicators exist and that assets associated with a particular operation are impaired. Evaluating impairment also requires us to estimate future operating results and cash flows, which also require judgment by management. Any resulting impairment loss could have a material adverse impact on our financial condition and results of operations.
Costs Associated with Exit or Disposal Activities or Restructurings, Policy [Policy Text Block]	Restructuring Our restructuring and other costs, net include primarily items such as restructuring portions of our operations, acquisition costs, divestiture costs and integration costs. We have restructured portions of our operations from time to time, have current restructuring initiatives taking place, and it is possible that we may engage in future restructuring activities. Identifying and calculating the cost to exit these operations requires certain assumptions to be made, the most significant of which are anticipated future liabilities, including severance costs, leases and other contractual obligations, and the adjustment of property, plant and equipment to net realizable value. We believe our estimates are reasonable, considering our knowledge of the industries we operate in, previous experience in exiting activities and valuations we may obtain from independent third parties. Although our estimates have been reasonably accurate in the past, significant judgment is required, and these estimates and assumptions may change as additional information becomes available and facts or circumstances change.
Business Combinations Policy [Policy Text Block]	Business Combinations From time to time, we may enter into business combinations. In accordance with ASC 805, “ Business Combinations ”, we generally recognize the identifiable assets acquired, the liabilities assumed, and any noncontrolling interests in an acquiree at their fair values as of the date of acquisition. We measure goodwill as the excess of consideration transferred, which we also measure at fair value, over the net of the acquisition date fair values of the identifiable assets acquired and liabilities assumed. The acquisition method of accounting requires us to make significant estimates and assumptions regarding the fair values of the elements of a business combination as of the date of acquisition, including the fair values of identifiable intangible assets, deferred tax asset valuation allowances, liabilities including those related to debt, pensions and other postretirement plans, uncertain tax positions, contingent consideration and contingencies. This method also requires us to refine these estimates over a measurement period not to exceed one year to reflect new information obtained about facts and circumstances that existed as of the acquisition date that, if known, would have affected the measurement of the amounts recognized as of that date. If we are required to adjust provisional amounts that we have recorded for the fair values of assets and liabilities in connection with acquisitions, these adjustments could have a material impact on our financial condition and results of operations. Significant estimates and assumptions in estimating the fair value of acquired technology, customer relationships, and other identifiable intangible assets include future cash flows that we expect to generate from the acquired assets. If the subsequent actual results and updated projections of the underlying business activity change compared with the assumptions and projections used to develop these values, we could record impairment charges. In addition, we have estimated the economic lives of certain acquired assets and these lives are used to calculate depreciation and amortization expense. If our estimates of the economic lives change, depreciation or amortization expenses could be increased or decreased, or the acquired asset could be impaired.
Fair Value of Financial Instruments, Policy [Policy Text Block]	Fair Value of Financial Instruments and Nonfinancial Assets and Liabilities We estimate fair values in accordance with ASC 820 “Fair Value Measurement. ” We define fair value as the price that would be received from the sale of an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Financial instruments not recognized at fair value on a recurring or nonrecurring basis include cash and cash equivalents, accounts receivables, certain other current assets, short-term debt, accounts payable, certain other current liabilities and long-term debt. With the exception of long-term debt, the carrying amounts of these financial instruments approximate their fair values due to their short maturities. The fair values of our long-term debt are estimated using quoted market prices or are based on the discounted value of future cash flows. We disclose the fair value of long-term debt in “Note 11. Debt” and our pension and postretirement assets and liabilities in “Note 15. Retirement Plans” . We have, or from time to time may have, financial instruments recognized at fair value including Supplemental Plans that are nonqualified deferred compensation plans pursuant to which assets are invested primarily in mutual funds, interest rate derivatives, commodity derivatives or other similar class of assets or liabilities, the fair value of which are not significant. We measure the fair value of our mutual fund investments based on quoted prices in active markets, and our derivative contracts, if any, based on discounted cash flows. We measure certain nonfinancial assets and nonfinancial liabilities at fair value on a nonrecurring basis. These assets and liabilities include cost and equity method investments when they are deemed to be other-than-temporarily impaired, assets acquired and liabilities assumed in a merger or an acquisition or in a nonmonetary exchange, and property, plant and equipment and goodwill and other intangible assets that are written down to fair value when they are held for sale or determined to be impaired. Given the nature of nonfinancial assets and liabilities, evaluating their fair value from the perspective of a market participant is inherently complex. Assumptions and estimates about future values can be affected by a variety of internal and external factors. Changes in these factors may require us to revise our estimates and could result in future impairment charges for goodwill and acquired intangible assets, or retroactively adjust provisional amounts that we have recorded for the fair values of assets and liabilities in connection with business combinations. These adjustments could have a material impact on our financial condition and results of operations. We discuss fair values in more detail in “Note 12. Fair Value” .
Derivatives, Policy [Policy Text Block]	Derivatives We are exposed to interest rate risk, commodity price risk and foreign currency exchange risk. To manage these risks, from time to time and to varying degrees, we may enter into a variety of financial derivative transactions and certain physical commodity transactions that are determined to be derivatives. Interest rate swaps may be entered into to manage the interest rate risk associated with a portion of our outstanding debt. Interest rate swaps are either designated for accounting purposes as cash flow hedges of forecasted floating interest payments on variable rate debt or fair value hedges of fixed rate debt, or we may elect not to treat them as accounting hedges. Swaps or forward contracts on certain commodities may be entered into to manage the price risk associated with forecasted purchases or sales of those commodities. In addition, certain commodity financial derivative contracts and physical commodity contracts that are determined to be derivatives may not be designated as accounting hedges because either they do not meet the criteria for treatment as accounting hedges under ASC 815, “Derivatives and Hedging”, or we elect not to treat them as accounting hedges under ASC 815. We may also enter into forward contracts to manage our exposure to fluctuations in foreign currency rates with respect to transactions denominated in currencies such as Canadian dollars, the Euro or Brazilian Real. These also can either be designated for accounting purposes as cash flow hedges or not so designated. Outstanding financial derivative instruments expose us to credit loss in the event of nonperformance by the counterparties to the derivative agreements. Our credit exposure related to these financial instruments is represented by the fair value of contracts reported as assets. We manage our exposure to counterparty credit risk through minimum credit standards, diversification of counterparties and procedures to monitor concentrations of credit risk. We may enter into financial derivative contracts that may contain credit-risk-related contingent features which could result in a counterparty requesting immediate payment or demanding immediate and ongoing full overnight collateralization on derivative instruments in net liability positions. For financial derivative instruments that are designated as a cash flow hedge for accounting purposes, the effective portion of the gain or loss on the financial derivative instrument is reported as a component of other comprehensive income and reclassified into earnings in the same line item associated with the forecasted transaction, and in the same period or periods during which the forecasted transaction affects earnings. Gains and losses on the financial derivative representing either hedge ineffectiveness or hedge components excluded from the assessment of effectiveness are recognized in current earnings. We have at times entered into interest rate swap agreements that effectively modified our exposure to interest rate risk by converting a portion of our interest payments on floating rate debt to a fixed rate basis, thus reducing the impact of interest rate changes on future interest expense. These agreements typically involved the receipt of floating rate amounts in exchange for fixed interest rate payments over the life of the agreements without an exchange of the underlying principal amount. At September 30, 2017 , there were no interest rate or commodity derivatives outstanding, and the notional amount of foreign currency derivatives were $ 47.8 million . At September 30, 2016 , there were no foreign currency, interest rate or commodity derivatives outstanding.
Health Care Costs, Policy [Policy Text Block]	Health Insurance We are self-insured for the majority of our group health insurance costs. However, we seek to limit our health insurance costs by entering into certain stop loss insurance coverage. Due to mergers, acquisitions and other factors, we may have plans that do not include stop loss insurance. We calculate our group health insurance reserve on an undiscounted basis based on estimated reserve rates. We utilize claims lag data provided by our claims administrators to compute the required estimated reserve rate. We calculate our average monthly claims paid using the actual monthly payments during the trailing 12-month period. At that time, we also calculate our required reserve using the reserve rates discussed above. While we believe that our assumptions are appropriate, significant differences in our actual experience or significant changes in our assumptions may materially affect our group health insurance costs.
Workers Compensation, Policy [Policy Text Block]	Workers’ Compensation We purchase large risk deductible workers’ compensation policies for the majority of our workers’ compensation liabilities that are subject to various deductibles to limit our exposure. We calculate our workers’ compensation reserves on an undiscounted basis based on estimated actuarially calculated development factors. While we believe that our assumptions are appropriate, significant differences in our actual experience or significant changes in our assumptions may materially affect our workers' compensation costs.
Income Tax, Policy [Policy Text Block]	Income Taxes We account for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial statement carrying amount and the tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. All deferred tax assets and liabilities are classified as noncurrent in our consolidated balance sheet in accordance with ASU 2015-17. We adopted these provisions prospectively on December 31, 2015, and prior periods were not retrospectively adjusted. We record net deferred tax assets to the extent we believe these assets will more likely than not be realized. In making such determination, we consider all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax planning strategies, recent financial operations and their associated valuation allowances, if any. In the event we were to determine that we would be able to realize or not realize our deferred income tax assets in the future in their net recorded amount, we would make an adjustment to the valuation allowance, which would reduce or increase the provision for income taxes, respectively. Certain provisions of ASC 740, “Income Taxes ” provide that a tax benefit from an uncertain tax position may be recognized when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on the technical merits. Income tax positions must meet a more likely than not recognition threshold at the effective date to be recognized. See “ Note 14. Income Taxes. ”
Pension and Other Postretirement Plans, Policy [Policy Text Block]	Pension and Other Postretirement Benefits We account for pension and other postretirement benefits in accordance with ASC 715, “ Compensation — Retirement Benefits ”. Accordingly, we recognize the funded status of our pension plans as assets or liabilities in our consolidated balance sheets. The funded status is the difference between our projected benefit obligations and fair value of plan assets. The determination of our obligation and expense for pension and other postretirement benefits is dependent on our selection of certain assumptions used by actuaries in calculating such amounts. We describe these assumptions in “Note 15. Retirement Plans,” which include, among others, the discount rate, expected long-term rates of return on plan assets and rates of increase in compensation levels. As provided under ASC 715, we defer actual results that differ from our assumptions, i.e. actuarial gains and losses, and amortize the difference over future periods. Therefore, these differences generally affect our recognized expense and funding requirements in future periods. Actuarial gains and losses occur when actual experience differs from the estimates used to determine the components of net periodic pension cost and when certain assumptions used to determine the fair value of the plan assets or projected benefit obligation are updated, such as but not limited to, changes in the discount rate, plan amendments, differences between actual and expected returns on plan assets, mortality assumptions and plan remeasurement. The amount of unrecognized actuarial gains and losses recognized in the current year’s operations is based on amortizing the unrecognized gains or losses for each plan that exceed the larger of 10% of the projected benefit obligation or the fair value of plan assets, also known as “the corridor”. The amount of unrecognized gain or loss that exceeds the corridor is amortized over the average future service of the plan participants or the average life expectancy of inactive plan participants for plans where all or almost all of the plan participants are inactive. While we believe that our assumptions are appropriate, significant differences in our actual experience or significant changes in our assumptions may materially affect our pension and other postretirement benefit obligations and our future expense.
Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]	Share-Based Compensation We recognize expense for share-based compensation plans based on the estimated fair value of the related awards in accordance with ASC 718, “ Compensation — Stock Compensation ”. Pursuant to our incentive stock plans, we can grant options and restricted stock, SARs and restricted stock units to employees and our non-employee directors. The grants generally vest over a period of up to three years depending on the nature of the award, except for non-employee director grants, which typically vest over a period of up to one year. Our restricted stock grants to employees generally contain performance or market conditions that must be met in conjunction with a service requirement for the shares to vest. We charge compensation under the plan to earnings over each increment’s individual restriction period. See “Note 17. Share-Based Compensation” for additional information.
Asset Retirement Obligation [Policy Text Block]	Asset Retirement Obligations The Company accounts for asset retirement obligations in accordance with ASC 410, “ Asset Retirement and Environmental Obligations ”. A liability and an asset are recorded equal to the present value of the estimated costs associated with the retirement of long-lived assets where a legal or contractual obligation exists and the liability can be reasonably estimated. The liability is accreted over time and the asset is depreciated over the remaining life of the related asset. Upon settlement of the liability, we will recognize a gain or loss for any difference between the settlement amount and the liability recorded. Asset retirement obligations with indeterminate settlement dates are not recorded until such time that a reasonable estimate may be made. Our asset retirement obligations consist primarily of landfill closure and post-closure costs at certain of our mills. At September 30, 2017 and September 30, 2016 , we had recorded liabilities of $70.5 million and $78.9 million , respectively.
Maintenance Cost, Policy [Policy Text Block]	Repair and Maintenance Costs We expense routine repair and maintenance costs as we incur them. We defer certain expenses we incur during planned major maintenance activities and recognize the expenses ratably over the shorter of the estimated interval until the next major maintenance activity or the life of the deferred item. This maintenance is generally performed every twelve to twenty-four months and has a significant impact on our results of operations in the period performed primarily due to lost production during the maintenance period.
Foreign Currency Transactions and Translations Policy [Policy Text Block]	Foreign Currency We translate the assets and liabilities of our foreign operations from their functional currency into U.S. dollars at the rate of exchange in effect as of the balance sheet date. We reflect the resulting translation adjustments in equity. We translate the revenues and expenses of our foreign operations at a daily average rate prevailing for each month during the fiscal year. We include gains or losses from foreign currency transactions, such as those resulting from the settlement of foreign receivables or payables, in the consolidated statements of operations.
Environmental Costs, Policy [Policy Text Block]	Environmental Remediation Costs We accrue for losses associated with our environmental remediation obligations when it is probable that we have incurred a liability and the amount of the loss can be reasonably estimated. We generally recognize accruals for estimated losses from our environmental remediation obligations no later than completion of the remedial feasibility study and adjust such accruals as further information develops or circumstances change. We recognize recoveries of our environmental remediation costs from other parties as assets when we deem their receipt probable. See “ Note 19. Commitments and Contingencies. ”

Description of Business and S35

Description of Business and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Sep. 30, 2017
Description of Business and Summary of Significant Accounting Policies [Abstract]
Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]	The following table represents a summary of the changes in the reserve for allowance for doubtful accounts, returns and allowances and cash discounts for fiscal 2017 , 2016 and 2015 (in millions): 2017 2016 2015 Balance at beginning of fiscal year $ 36.5 $ 29.5 $ 25.1 Reduction in sales and charges to costs and expenses 215.6 200.8 166.6 Deductions (206.3 ) (193.8 ) (162.2 ) Balance at end of fiscal year $ 45.8 $ 36.5 $ 29.5
Property, Plant and Equipment, Estimated Useful Lives [Table Text Block]	For financial reporting purposes, we provide depreciation and amortization primarily on a straight-line method generally over the estimated useful lives of the assets as follows: Buildings and building improvements 15-40 years Machinery and equipment 3-25 years Transportation equipment 3-8 years

Earnings per Share (Tables)

Earnings per Share (Tables)	12 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Schedule of earnings per share, basic and diluted	The following table sets forth the computation of basic and diluted earnings per share under the two-class method (in millions, except per share data): September 30, 2017 2016 2015 Basic earnings (loss) per share: Numerator: Income from continuing operations $ 698.6 $ 154.8 $ 501.2 Less: Net loss (income) from continuing operations attributable to noncontrolling interest 9.6 (2.1 ) (3.3 ) Income available to common stockholders, before discontinued operations 708.2 152.7 497.9 Less: Distributed and undistributed income available to participating securities (0.1 ) — — Distributed and undistributed income attributable to common stockholders, before discontinued operations 708.1 152.7 497.9 (Loss) income from discontinued operations (1) — (549.0 ) 9.2 Net income (loss) attributable to common stockholders $ 708.1 $ (396.3 ) $ 507.1 Denominator: Basic weighted average shares outstanding 252.2 254.0 170.6 Basic earnings per share from continuing operations $ 2.81 $ 0.60 $ 2.92 Basic (loss) earnings per share from discontinued operations — (2.16 ) 0.05 Basic earnings (loss) per share attributable to common stockholders $ 2.81 $ (1.56 ) $ 2.97 Diluted earnings (loss) per share : Numerator: Income from continuing operations $ 698.6 $ 154.8 $ 501.2 Less: Net loss (income) from continuing operations attributable to noncontrolling interest 9.6 (2.1 ) (3.3 ) Income available to common stockholders, before discontinued operations 708.2 152.7 497.9 Less: Distributed and undistributed income available to participating securities (0.1 ) — — Distributed and undistributed income attributable to common stockholders, before discontinued operations 708.1 152.7 497.9 (Loss) Income from discontinued operations (1) — (549.0 ) 9.2 Net income (loss) attributable to common stockholders $ 708.1 $ (396.3 ) $ 507.1 Denominator: Basic weighted average shares outstanding 252.2 254.0 170.6 Effect of dilutive stock options and non-participating securities 3.5 3.9 2.7 Diluted weighted average shares outstanding 255.7 257.9 173.3 Diluted earnings per share from continuing operations $ 2.77 $ 0.59 $ 2.87 Diluted (loss) earnings per share from discontinued operations — (2.13 ) 0.06 Diluted earnings (loss) per share attributable to common stockholders $ 2.77 $ (1.54 ) $ 2.93 (1) Net of income attributable to noncontrolling interests of discontinued operations of $4.3 million and $1.4 million for the fiscal years ended September 30, 2016 and 2015.

Other Comprehensive Income (L37

Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Sep. 30, 2017
Other Comprehensive Income (Loss) [Abstract]
Schedule of accumulated other comprehensive income (loss)	The following table summarizes the changes in accumulated other comprehensive loss by component for the fiscal years ended September 30, 2017 and 2016 (in millions): Deferred Loss on Cash Flow Hedges Defined Benefit Pension and Postretirement Plans Foreign Currency Items Available for Sale Security Total (1) Balance at September 30, 2015 $ (1.4 ) $ (540.7 ) $ (238.1 ) $ — $ (780.2 ) Other comprehensive (loss) income before reclassifications (0.4 ) (222.2 ) 109.9 — (112.7 ) Amounts reclassified from accumulated other comprehensive loss (2) 1.2 237.2 20.2 — 258.6 Net current period other comprehensive income 0.8 15.0 130.1 — 145.9 Separation of Specialty Chemicals business 0.4 1.9 5.6 — 7.9 Balance at September 30, 2016 $ (0.2 ) $ (523.8 ) $ (102.4 ) $ — $ (626.4 ) Other comprehensive income before reclassifications — 22.8 80.8 0.7 104.3 Amounts reclassified from accumulated other comprehensive (income) loss (0.5 ) 35.6 — — 35.1 Sale of HH&B — 2.9 26.8 — 29.7 Net current period other comprehensive (loss) income (0.5 ) 61.3 107.6 0.7 169.1 Balance at September 30, 2017 $ (0.7 ) $ (462.5 ) $ 5.2 $ 0.7 $ (457.3 ) (1) All amounts are net of tax and noncontrolling interest. (2) Amounts reclasssified from accumulated other comprehensive loss for defined benefit pension and postretirement plans in fiscal 2016 includes the pension risk transfer expense, net of tax.
Schedule of other comprehensive income (loss)	A summary of the components of other comprehensive income (loss), including noncontrolling interest, for the years ended September 30, 2017 , 2016 and 2015 , is as follows (in millions): Fiscal 2017 Pre-Tax Amount Tax Net of Tax Amount Foreign currency translation gain $ 80.7 $ — $ 80.7 Sale of HH&B, foreign currency 26.8 — 26.8 Reclassification adjustment of net gain on cash flow hedges included in earnings (0.8 ) 0.3 (0.5 ) Net actuarial gain arising during period 34.1 (11.9 ) 22.2 Amortization and settlement recognition of net actuarial loss 56.4 (20.4 ) 36.0 Prior service credit arising during the period 1.0 (0.3 ) 0.7 Amortization of prior service credit (0.4 ) 0.2 (0.2 ) Unrealized gain on available for sale security 0.7 — 0.7 Sale of HH&B, defined benefit pension plans 4.2 (1.3 ) 2.9 Consolidated other comprehensive income 202.7 (33.4 ) 169.3 Less: Other comprehensive income attributable to noncontrolling interests (0.2 ) — (0.2 ) Other comprehensive income attributable to common stockholders $ 202.5 $ (33.4 ) $ 169.1 Fiscal 2016 Pre-Tax Amount Tax Net of Tax Amount Foreign currency translation gain $ 109.8 $ — $ 109.8 Deferred loss on cash flow hedges (0.7 ) 0.3 (0.4 ) Reclassification adjustment of net loss on cash flow hedges included in earnings 1.9 (0.7 ) 1.2 Net actuarial loss arising during period (354.0 ) 129.4 (224.6 ) Amortization and settlement recognition of net actuarial loss (1) 379.7 (143.2 ) 236.5 Prior service credit arising during the period 2.3 (0.9 ) 1.4 Amortization of prior service cost 1.8 (0.7 ) 1.1 Sale of foreign subsidiary 20.2 — 20.2 Consolidated other comprehensive income 161.0 (15.8 ) 145.2 Less: Other comprehensive loss attributable to noncontrolling interests 0.7 — 0.7 Other comprehensive income attributable to common stockholders $ 161.7 $ (15.8 ) $ 145.9 Fiscal 2015 Pre-Tax Amount Tax Net of Tax Amount Foreign currency translation loss $ (242.0 ) $ — $ (242.0 ) Deferred loss on cash flow hedges (2.6 ) 1.0 (1.6 ) Reclassification adjustment of net loss on cash flow hedges included in earnings 0.7 (0.3 ) 0.4 Net actuarial loss arising during period (81.5 ) 28.9 (52.6 ) Amortization and settlement recognition of net actuarial loss 48.1 (17.8 ) 30.3 Prior service cost arising during period (25.0 ) 9.6 (15.4 ) Amortization of prior service credit (7.5 ) 2.9 (4.6 ) Consolidated other comprehensive loss (309.8 ) 24.3 (285.5 ) Less: Other comprehensive loss attributable to noncontrolling interests 0.6 — 0.6 Other comprehensive loss attributable to common stockholders $ (309.2 ) $ 24.3 $ (284.9 ) (1) Includes pension risk transfer expense.
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]	The following table summarizes the reclassifications out of accumulated other comprehensive loss by component for the fiscal years ended September 30, 2017 and 2016 (in millions): Years Ended September 30, 2017 2016 Pretax Tax Net of Tax Pretax Tax Net of Tax Amortization of defined benefit pension and postretirement items: (1) Actuarial losses (2)(3) $ (56.3 ) $ 20.4 $ (35.9 ) $ (379.4 ) $ 143.2 $ (236.2 ) Prior service credits (costs) (2) 0.5 (0.2 ) 0.3 (1.7 ) 0.7 (1.0 ) Sale of HH&B (4) (4.2 ) 1.3 (2.9 ) — — — Subtotal defined benefit plans (60.0 ) 21.5 (38.5 ) (381.1 ) 143.9 (237.2 ) Foreign currency translation adjustments: (1) Sale of HH&B (4) (26.8 ) — (26.8 ) — — — Sale of foreign subsidiary (5) — — — (20.2 ) — (20.2 ) Subtotal foreign currency translation adjustment (26.8 ) — (26.8 ) (20.2 ) — (20.2 ) Derivative Instruments: (1) Commodity currency cash flow hedges (6) — — — (1.5 ) 0.5 (1.0 ) Foreign currency cash flow hedges (7) 0.8 (0.3 ) 0.5 (0.4 ) 0.2 (0.2 ) Subtotal derivative instruments 0.8 (0.3 ) 0.5 (1.9 ) 0.7 (1.2 ) Total reclassifications for the period $ (86.0 ) $ 21.2 $ (64.8 ) $ (403.2 ) $ 144.6 $ (258.6 ) (1) Amounts in parentheses indicate charges to earnings. Amounts pertaining to noncontrolling interests are excluded. (2) These accumulated other comprehensive income components are included in the computation of net periodic pension cost. See “ Note 15. Retirement Plans ” for additional details. (3) Fiscal 2016 includes pension risk transfer expense. (4) Included in gain on sale of HH&B. (5) These accumulated other comprehensive income components are included in interest income and other income (expense), net. (6) These accumulated other comprehensive income components are included in cost of goods sold. (7) These accumulated other comprehensive income components are included in net sales.

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Sep. 30, 2017
Inventories [Abstract]
Schedule of inventories	Inventories are as follows (in millions): September 30, 2017 2016 Finished goods and work in process $ 905.0 $ 800.6 Raw materials 614.2 535.7 Supplies and spare parts 360.7 335.7 Inventories at FIFO cost 1,879.9 1,672.0 LIFO reserve (82.6 ) (33.8 ) Net inventories $ 1,797.3 $ 1,638.2

Property, Plant and Equipment39

Property, Plant and Equipment (Tables)	12 Months Ended
	Sep. 30, 2017
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment [Table Text Block]	Property, plant and equipment consists of the following (in millions): September 30, 2017 2016 Property, plant and equipment at cost: Land and buildings $ 2,034.3 $ 2,307.9 Machinery and equipment 11,349.7 10,672.9 Forestlands and mineral rights 208.3 201.1 Transportation equipment 30.7 27.6 Leasehold improvements 59.5 62.4 13,682.5 13,271.9 Less: accumulated depreciation and amortization (4,564.2 ) (3,977.6 ) Property, plant and equipment, net $ 9,118.3 $ 9,294.3

Acquisitions (Tables)

Acquisitions (Tables)	12 Months Ended
	Sep. 30, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Purchase price allocation, opening balance	The following table summarizes the fair values of the assets acquired and liabilities assumed by major class of assets and liabilities as of the acquisition date, as well as adjustments made during fiscal 2016 (referred to as “measurement period adjustments”) (in millions): Amounts Recognized as of the Acquisition Date Measurement Period Adjustments (1) Amounts Recognized as of Acquisition Date (as Adjusted) (2) Cash and cash equivalents $ 265.7 $ — $ 265.7 Current assets, excluding cash and cash equivalents 1,858.8 (0.5 ) 1,858.3 Property, plant and equipment 3,991.5 19.3 4,010.8 Prepaid pension asset 1,407.8 (9.9 ) 1,397.9 Goodwill 3,817.3 44.7 3,862.0 Intangible assets 2,994.2 — 2,994.2 Restricted assets held by special purpose entities 1,302.0 — 1,302.0 Other long-term assets 363.8 18.0 381.8 Total assets acquired 16,001.1 71.6 16,072.7 Current portion of debt 62.3 74.8 137.1 Current liabilities 1,099.4 (45.6 ) 1,053.8 Long-term debt due after one year 2,090.6 18.3 2,108.9 Non-recourse liabilities held by special purpose entities 1,181.0 — 1,181.0 Accrued pension and other long-term benefits 235.1 — 235.1 Deferred income tax liabilities 2,366.7 (11.0 ) 2,355.7 Other long-term liabilities 520.0 35.1 555.1 Noncontrolling interest 159.3 — 159.3 Total liabilities and noncontrolling interest assumed 7,714.4 71.6 7,786.0 Net assets acquired (3) $ 8,286.7 $ — $ 8,286.7 (1) The measurement period adjustments recorded in fiscal 2016 did not have a significant impact on our consolidated statements of operations for fiscal 2016 or 2015. In addition, these adjustments did not have a significant impact on our consolidated balance sheet as of September 30, 2015. Therefore, we have recorded the cumulative impact in fiscal 2016 and have not retrospectively adjusted the comparative 2015 financial information presented herein. (2) The measurement period adjustments were due primarily to refinements to third party appraisals and carrying amounts of certain assets and liabilities as well as adjustments to certain tax accounts based on, among other things, adjustments to deferred tax liabilities, including any appraisal adjustments, analysis of the tax basis of acquired assets and liabilities, other tax adjustments and the classification of supplier financing arrangements. The net impact of the measurement period adjustments resulted in a net increase to goodwill. (3) The net assets acquired include the Specialty Chemicals business, which was separated from WestRock on May 15, 2016 . See “ Note 7. Discontinued Operations ” for additional information.
Schedule of Finite-Lived Intangible Assets Acquired as Part of Business Combination	The following table summarizes the weighted average life and gross carrying amount relating to intangible assets recognized in the Combination, excluding goodwill (in millions): Weighted Avg. Life Gross Carrying Amount Customer relationships 19.2 $ 2,881.7 Patents 9.8 57.2 Trademarks and tradenames 4.5 52.9 Favorable contracts 8.2 2.4 Total 18.8 $ 2,994.2 The following table summarizes the weighted average life and the preliminary allocation to intangible assets recognized in the MPS Acquisition, excluding goodwill (in millions): Weighted Avg. Life Amounts Recognized as of the Acquisition Date Customer relationships 14.6 $ 999.9 Trademarks and tradenames 3.0 15.2 Photo library 10.0 2.5 Total 14.4 $ 1,017.6
Schedule of pro forma information related to acquisition	The following unaudited pro forma information reflects our consolidated results of operations as if the Combination had taken place on October 1, 2013. The unaudited pro forma information is not necessarily indicative of the results of operations that we would have reported had the transaction actually occurred at the beginning of these periods nor is it necessarily indicative of future results. The unaudited pro forma financial information does not reflect the impact of future events that may occur after the Combination, including, but not limited to, anticipated costs savings from synergies or other operational improvements. The net sales have been adjusted to reflect the discontinued operations of the Specialty Chemicals business. Year Ended September 30, 2015 (Unaudited, in millions) Net sales $ 14,347.0 Net income attributable to common stockholders $ 666.3

Discontinued Operations (Tables

Discontinued Operations (Tables)	12 Months Ended
	Sep. 30, 2017
Disposal Groups, Including Discontinued Operations [Table Text Block]	The following table presents the financial results of Specialty Chemicals’ discontinued operations (in millions): Fiscal Year Ended September 30, 2016 2015 Net sales $ 533.7 $ 256.5 Cost of goods sold 387.5 184.0 Gross profit 146.2 72.5 Selling, general and administrative, excluding intangible amortization 65.6 27.4 Selling, general and administrative intangible amortization 28.8 11.5 Restructuring and other costs, net 49.5 6.6 Impairment of Specialty Chemicals goodwill and intangibles 579.4 — Operating (loss) profit (577.1 ) 27.0 Interest income (expense) and other income (expense), net 0.1 1.1 (Loss) income from discontinued operations before income taxes (577.0 ) 28.1 Income tax benefit (expense) 32.3 (17.5 ) (Loss) income from discontinued operations $ (544.7 ) $ 10.6 The following table presents the significant non-cash items and capital expenditures for Specialty Chemicals’ that are included in the Consolidated Statements of Cash Flows (in millions): Fiscal Year Ended September 30, 2016 2015 Depreciation, depletion and amortization $ 57.2 $ 22.0 Impairment of Specialty Chemicals goodwill and intangibles $ 579.4 $ — Capital expenditures $ (45.2 ) $ (28.6 )

Restructuring and Other Costs42

Restructuring and Other Costs, Net (Tables)	12 Months Ended
	Sep. 30, 2017
Restructuring and Other Costs, Net [Abstract]
Schedule of restructuring and other costs, net	The following table summarizes our Restructuring and other costs, net for fiscal 2017 , 2016 and 2015 (in millions): Fiscal 2017 Fiscal 2016 Fiscal 2015 Restructuring $ 113.4 $ 294.9 $ 60.3 Other 83.3 71.5 80.5 Restructuring and Other Costs, net $ 196.7 $ 366.4 $ 140.8
Restructuring and Related Costs [Table Text Block]	The following table presents a summary of restructuring charges related to active restructuring initiatives that we incurred during the last three fiscal years, the cumulative recorded amount since we started the initiative, and our estimate of the total we expect to incur (in millions): Fiscal 2017 Fiscal 2016 Fiscal 2015 Cumulative Total Expected Corrugated Packaging Net property, plant and equipment costs $ 1.4 $ 184.5 $ 1.3 $ 221.0 $ 221.0 Severance and other employee costs 3.3 17.4 0.4 43.2 45.1 Equipment and inventory relocation costs 1.9 0.3 1.1 6.5 9.0 Facility carrying costs 5.4 18.9 3.0 36.4 39.7 Other costs (1.2 ) 9.1 2.2 20.5 20.5 Restructuring total $ 10.8 $ 230.2 $ 8.0 $ 327.6 $ 335.3 Consumer Packaging Net property, plant and equipment costs $ 28.3 $ 3.8 $ 0.9 $ 37.5 $ 37.5 Severance and other employee costs 26.4 4.6 1.8 34.4 34.4 Equipment and inventory relocation costs 2.8 1.1 0.5 4.9 7.4 Facility carrying costs 0.7 0.5 0.9 2.4 3.8 Other costs (1) 20.2 — 0.3 20.7 20.7 Restructuring total $ 78.4 $ 10.0 $ 4.4 $ 99.9 $ 103.8 Land and Development Net property, plant and equipment costs $ 1.8 $ — $ — $ 1.8 $ 1.8 Severance and other employee costs 2.8 10.6 — 13.4 14.5 Restructuring total $ 4.6 $ 10.6 $ — $ 15.2 $ 16.3 Corporate Net property, plant and equipment costs $ 0.1 $ 1.2 $ — $ 1.4 $ 1.4 Severance and other employee costs 14.8 36.9 48.2 99.9 99.9 Other costs 4.7 6.0 (0.3 ) 10.4 10.4 Restructuring total $ 19.6 $ 44.1 $ 47.9 $ 111.7 $ 111.7 Total Net property, plant and equipment costs $ 31.6 $ 189.5 $ 2.2 $ 261.7 $ 261.7 Severance and other employee costs 47.3 69.5 50.4 190.9 193.9 Equipment and inventory relocation costs 4.7 1.4 1.6 11.4 16.4 Facility carrying costs 6.1 19.4 3.9 38.8 43.5 Other costs 23.7 15.1 2.2 51.6 51.6 Restructuring total $ 113.4 $ 294.9 $ 60.3 $ 554.4 $ 567.1 (1) Includes a $17.6 million impairment of a customer relationship intangible in fiscal 2017 related to an exited product line.
Schedule of Restructuring and Other Costs Reserve By Type of Cost Text Block [Table Text Block]	The following table represents a summary of and the changes in the restructuring accrual, which is primarily composed of lease commitments, accrued severance and other employee costs, and a reconciliation of the restructuring accrual charges to the line item “Restructuring and other costs, net” on our Consolidated Statements of Operations for fiscal 2017 , 2016 and 2015 (in millions): 2017 2016 2015 Accrual at beginning of fiscal year $ 44.8 $ 21.4 $ 10.9 Accruals acquired in purchase accounting 3.5 — 2.9 Additional accruals 63.2 75.3 37.6 Payments (53.3 ) (51.9 ) (31.4 ) Adjustment to accruals (10.8 ) — 1.4 Accrual at end of fiscal year $ 47.4 $ 44.8 $ 21.4 Reconciliation of accruals and charges to restructuring and other costs, net (in millions): 2017 2016 2015 Additional accruals and adjustments to accruals (see table above) $ 52.4 $ 75.3 $ 39.0 Acquisition costs 27.1 8.9 44.4 Divestiture costs 9.8 0.5 — Integration costs 41.2 59.8 36.8 Net property, plant and equipment 31.6 189.5 2.2 Severance and other employee costs 3.8 11.5 12.7 Equipment and inventory relocation costs 4.7 1.4 1.6 Facility carrying costs 6.1 19.5 3.9 Other costs 20.0 — 0.2 Total restructuring and other costs, net $ 196.7 $ 366.4 $ 140.8
Schedule of Restructuring Costs Included in Other Costs [Table Text Block]	The following table presents our acquisition, divestiture and integration costs that we incurred during the last three fiscal years (in millions): Fiscal 2017 Fiscal 2016 Fiscal 2015 Acquisition costs $ 27.1 $ 8.9 $ 44.4 Divestiture costs 9.8 0.5 — Integration costs 46.4 62.1 36.1 Other total $ 83.3 $ 71.5 $ 80.5

Other Intangible Assets (Tables

Other Intangible Assets (Tables)	12 Months Ended
	Sep. 30, 2017
Other Intangible Assets [Abstract]
Schedule of Finite-Lived Intangible Assets [Table Text Block]	The gross carrying amount and accumulated amortization relating to intangible assets, excluding goodwill, is as follows (in millions, except weighted avg. life): September 30, 2017 2016 Weighted Avg. Life (in years) Gross Carrying Amount Accumulated Amortization Gross Carrying Amount Accumulated Amortization Customer relationships 16.7 $ 4,046.2 $ (806.0 ) $ 3,094.4 $ (610.5 ) Favorable contracts 9.6 48.2 (30.7 ) 48.9 (27.0 ) Technology and patents 10.7 31.8 (14.4 ) 55.4 (14.9 ) Trademarks and tradenames 16.3 74.7 (31.4 ) 65.0 (24.1 ) Non-compete agreements 2.0 2.5 (0.6 ) 0.2 (0.1 ) License costs 8.8 23.6 (14.6 ) 23.5 (11.5 ) Total 16.6 $ 4,227.0 $ (897.7 ) $ 3,287.4 $ (688.1 )
Estimated intangible asset future amortization expense	Estimated intangible asset amortization expense for the succeeding five fiscal years is as follows (in millions): Fiscal 2018 $ 294.1 Fiscal 2019 $ 292.1 Fiscal 2020 $ 281.3 Fiscal 2021 $ 234.6 Fiscal 2022 $ 225.3

Debt (Tables)

Debt (Tables)	12 Months Ended
	Sep. 30, 2017
Debt [Abstract]
Components of debt	The following were individual components of debt (in millions): September 30, 2017 September 30, 2016 Carrying Value Weighted Avg Interest Rate Carrying Value Weighted Avg Interest Rate Public bonds due fiscal 2017 to 2022 $ 1,484.5 4.2 % $ 1,651.0 3.9 % Public bonds due fiscal 2023 to 2027 1,368.8 3.6 % 411.8 4.3 % Public bonds due fiscal 2030 to 2033 975.5 5.2 % 987.5 4.7 % Public bonds due fiscal 2037 to 2047 178.8 6.3 % 179.2 6.0 % Term loan facilities 1,622.7 2.5 % 2,195.7 1.8 % Revolving credit facilities 436.4 1.1 % — N/A Receivables-backed financing facility 110.0 2.1 % — N/A Capital lease obligations 177.0 4.3 % 184.4 4.2 % Supplier financing and commercial card programs 130.3 N/A 106.0 N/A International and other debt 70.8 6.8 % 73.6 7.3 % Total debt 6,554.8 3.6 % 5,789.2 3.3 % Less current portion of debt 608.7 292.9 Long-term debt due after one year $ 5,946.1 $ 5,496.3
Schedule of aggregate maturities of debt	As of September 30, 2017 , the aggregate maturities of debt, excluding capital lease obligations, for the succeeding five fiscal years and thereafter are as follows (in millions): Fiscal 2018 $ 603.6 Fiscal 2019 724.5 Fiscal 2020 1,499.8 Fiscal 2021 — Fiscal 2022 1,000.0 Thereafter 2,309.2 Fair value of debt step-up, deferred financing costs and unamortized bond discounts 240.7 Total $ 6,377.8 As of September 30, 2017 , the aggregate maturities of capital lease obligations for the succeeding five fiscal years and thereafter are as follows (in millions): Fiscal 2018 $ 5.6 Fiscal 2019 4.5 Fiscal 2020 3.4 Fiscal 2021 2.1 Fiscal 2022 2.1 Thereafter 138.7 Fair value step-up 20.6 Total $ 177.0

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
	Sep. 30, 2017
Accounts Receivable Sales Agreement Rollforward [Line Items]
Accounts Receivable Sales Agreement Rollforward [Table Text Block]	The following table represents a summary of the activity under the A/R Sales Agreement for fiscal 2017 and 2016 (in millions): 2017 2016 Receivable from financial institution at beginning of fiscal year $ 13.8 $ 5.8 Receivables sold to the financial institution and derecognized 1,542.5 1,474.6 Receivables collected by financial institution (1,466.7 ) (1,367.2 ) Cash proceeds from financial institution (64.7 ) (99.4 ) Receivable from financial institution at September 30, $ 24.9 $ 13.8

Leases (Tables)

Leases (Tables)	12 Months Ended
	Sep. 30, 2017
Leases [Abstract]
Schedule of future minimum rental payments for operating leases	As of September 30, 2017 , future minimum lease payments under all noncancelable operating leases for the succeeding five fiscal years and thereafter are as follows (in millions): Fiscal 2018 $ 123.3 Fiscal 2019 103.5 Fiscal 2020 86.3 Fiscal 2021 68.8 Fiscal 2022 54.5 Thereafter 188.6 Total future minimum lease payments $ 625.0

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2017
Tax Provision [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]	The components of income (loss) from continuing operations before income taxes are as follows (in millions): Year Ended September 30, 2017 2016 2015 United States $ 481.9 $ (25.1 ) $ 571.3 Foreign 375.7 269.7 162.9 Income from continuing operations before income taxes $ 857.6 $ 244.6 $ 734.2
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	Income tax expense (benefit) from continuing operations consists of the following components (in millions): Year Ended September 30, 2017 2016 2015 Current income taxes: Federal $ 80.8 $ 98.3 $ 31.6 State 3.3 12.8 7.3 Foreign 95.3 87.0 38.6 Total current expense 179.4 198.1 77.5 Deferred income taxes: Federal 15.2 (131.5 ) 157.8 State (22.8 ) 6.9 (10.8 ) Foreign (12.8 ) 16.3 8.5 Total deferred (benefit) expense (20.4 ) (108.3 ) 155.5 Total income tax expense $ 159.0 $ 89.8 $ 233.0
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	The differences between the statutory federal income tax rate and our effective income tax rate from continuing operations are as follows: Year Ended September 30, 2017 2016 2015 Statutory federal tax rate 35.0 % 35.0 % 35.0 % Foreign rate differential (4.9 ) (5.5 ) (1.6 ) Adjustment and resolution of federal, state and foreign tax uncertainties (0.3 ) 0.2 0.3 State taxes, net of federal benefit 3.3 4.9 1.2 Research and development and other tax credits, net of valuation allowances and reserves (0.8 ) (6.1 ) (0.1 ) Income attributable to noncontrolling interest 0.4 0.8 (0.4 ) Domestic manufacturer’s deduction (2.0 ) (4.4 ) (2.6 ) Sale of HH&B (5.0 ) — — U.S. legal entity restructuring (3.3 ) — — Change in valuation allowance (3.3 ) 6.3 (0.8 ) Nondeductible transaction costs 1.0 0.4 1.0 Contribution of assets to Grupo Gondi joint venture — 3.4 — Nontaxable increased cash surrender value (1.5 ) (4.6 ) (0.1 ) Withholding taxes 0.4 2.0 — Brazilian net worth deduction (0.8 ) (2.0 ) (0.1 ) Other, net 0.3 6.3 (0.1 ) Effective tax rate 18.5 % 36.7 % 31.7 %
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	The tax effects of temporary differences that give rise to deferred income tax assets and liabilities consist of the following (in millions): September 30, 2017 2016 Deferred income tax assets: Accruals and allowances $ 40.6 $ 12.2 Employee related accruals and allowances 265.1 217.6 Pension obligations — 15.5 State net operating loss carryforwards 70.6 82.3 State credit carryforwards, net of federal benefit 54.4 56.1 U.S. and foreign tax credit carryforwards 135.9 185.1 Federal and foreign net operating loss carryforwards 204.1 119.3 Restricted stock and options 81.0 94.9 Other 32.8 44.4 Total 884.5 827.4 Deferred income tax liabilities: Property, plant and equipment 2,154.1 2,124.0 Deductible intangibles and goodwill 1,091.4 891.3 Inventory reserves 236.1 205.6 Deferred gain 405.2 432.1 Pension obligations 90.8 — Basis difference in joint ventures 57.1 96.0 Other 8.3 1.0 Total 4,043.0 3,750.0 Valuation allowances 219.1 177.2 Net deferred income tax liability $ 3,377.6 $ 3,099.8
Location of Deferred Taxes in Balance Sheet [Table Text Block]	Deferred taxes are recorded as follows in the consolidated balance sheet (in millions): September 30, 2017 2016 Long-term deferred tax asset (1) $ 32.6 $ 30.9 Long-term deferred tax liability 3,410.2 3,130.7 Net deferred income tax liability $ 3,377.6 $ 3,099.8 (1) The long-term deferred tax asset is presented in Other assets on the Consolidated Balance Sheets.
Summary of Valuation Allowance [Table Text Block]	The following table represents a summary of the valuation allowances against deferred tax assets for fiscal 2017 , 2016 and 2015 (in millions): 2017 2016 2015 Balance at beginning of fiscal year $ 177.2 $ 100.2 $ 65.1 Increases 54.3 24.8 2.7 Allowances related to purchase accounting (1) 12.4 63.0 40.0 Reductions (24.8 ) (10.8 ) (7.6 ) Balance at end of fiscal year $ 219.1 $ 177.2 $ 100.2 (1) Adjustments in fiscal 2017 relate to the MPS Acquisition. Adjustments in fiscal 2016 relate to the Combination and the SP Fiber Acquisition. Adjustments in fiscal 2015 relate to the Combination
Summary of Income Tax Contingencies [Table Text Block]	A reconciliation of the beginning and ending amount of gross unrecognized tax benefits is as follows (in millions): 2017 2016 2015 Balance at beginning of fiscal year $ 166.8 $ 106.6 $ 36.5 Additions related to purchase accounting (1) 7.7 16.5 82.9 Additions for tax positions taken in current year 5.0 30.3 2.4 Additions for tax positions taken in prior fiscal years 15.2 20.6 — Reductions for tax positions taken in prior fiscal years (25.6 ) (9.7 ) (3.7 ) Reductions due to settlement (2) (14.1 ) (1.3 ) — Additions (reductions) for currency translation adjustments 2.0 7.0 (11.5 ) Reductions as a result of a lapse of the applicable statute of limitations (8.1 ) (3.2 ) — Balance at end of fiscal year $ 148.9 $ 166.8 $ 106.6 (1) Adjustments in fiscal 2017 relate to the MPS Acquisition. Adjustments in fiscal 2016 relate to the Combination and the SP Fiber Acquisition. Adjustments in fiscal 2015 relate to the Combination. (2) Reductions due to settlement in fiscal 2017 relate to the settlement of federal and state audit examinations with taxing authorities.

Retirement Plans (Tables)

Retirement Plans (Tables)	12 Months Ended
	Sep. 30, 2017
Retirement Plans [Abstract]
Schedule of Allocation of Plan Assets [Table Text Block]	Target Allocations U.S. Plans Non-U.S. Plans 2017 2016 2017 2016 Equity investments 15 % 14 % 24 % 28 % Fixed income investments 70 % 71 % 65 % 59 % Short-term investments 1 % 1 % 1 % 1 % Other investments 14 % 14 % 10 % 12 % Total 100 % 100 % 100 % 100 % Our asset allocations by asset category at September 30 were as follows: U.S. Plans Non-U.S. Plans 2017 2016 2017 2016 Equity investments 13 % 15 % 26 % 29 % Fixed income investments 73 % 66 % 64 % 59 % Short-term investments 3 % 7 % 3 % 2 % Other investments 11 % 12 % 7 % 10 % Total 100 % 100 % 100 % 100 %
Schedule of Weighted-Average Assumptions Used [Table Text Block]	The weighted average assumptions used to measure the benefit plan obligations at September 30 were: Postretirement plans 2017 2016 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Discount rate 4.09% 6.51 % 4.04% 6.64 % Rate of compensation increase N/A 7.37 % N/A 3.14 % Weighted-average assumptions used in the calculation of benefit plan expense for fiscal years ended: Pension Plans 2017 2016 2015 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Discount rate 4.30% 3.08 % 4.70 % 3.89 % 4.52 % 4.00 % Rate of compensation increase 3.00% 3.09 % 2.50 % 3.10 % 2.54 % 3.00 % Expected long-term rate of return on plan assets 6.50% 6.03 % 5.88 % 6.34 % 7.11 % 6.88 % Weighted-average assumptions used in the calculation of benefit plan expense for fiscal years ended: Postretirement Plans 2017 2016 2015 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Discount rate 4.04% 6.64 % 4.70% 6.84 % 4.52 % 4.00 % Rate of compensation increase N/A 3.14 % N/A 3.10 % N/A 3.00 % The weighted average assumptions used to measure the benefit plan obligations at September 30, were: Pension Plans 2017 2016 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Discount rate 4.09% 3.26% 4.04% 3.08 % Rate of compensation increase 3.00% 3.17% 3.00% 3.09 %
Schedule of Changes in Benefit Obligations [Table Text Block]	The following table shows the changes in benefit obligation and plan assets, and the plan’s funded status for the years ended September 30 (in millions): Pension Plans 2017 2016 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Change in projected benefit obligation Benefit obligation at beginning of fiscal year $ 4,231.7 $ 925.2 $ 6,122.3 $ 865.1 Service cost 38.0 7.1 45.7 5.7 Interest cost 165.2 32.6 277.8 32.5 Amendments 3.5 — 1.4 — Actuarial (gain) loss (149.1 ) (57.6 ) 664.2 70.8 Plan participant contributions — 1.7 — 1.5 Special termination benefits 12.5 — 18.4 — Benefits paid (141.4 ) (65.1 ) (399.2 ) (57.5 ) Business combinations — 621.0 9.9 (0.6 ) Curtailments — — (2.7 ) (0.5 ) Settlements (229.3 ) (0.4 ) (2,484.6 ) (0.1 ) Foreign currency rate changes — 65.1 — 8.3 Other adjustments 10.8 — — — Business divestitures — (27.4 ) (21.5 ) — Benefit obligation at end of fiscal year $ 3,941.9 $ 1,502.2 $ 4,231.7 $ 925.2 Change in plan assets Fair value of plan assets at beginning of fiscal year $ 4,301.5 $ 774.1 $ 6,481.6 $ 711.8 Actual gain on plan assets 104.2 2.4 707.3 82.9 Employer contributions 15.3 19.2 16.1 31.4 Plan participant contributions — 1.7 — 1.5 Benefits paid (141.4 ) (65.1 ) (399.2 ) (57.5 ) Business combinations — 622.1 — — Settlements (229.3 ) (0.4 ) (2,484.6 ) (0.1 ) Business divestitures — (0.7 ) (19.7 ) — Foreign currency rate changes — 61.4 — 4.1 Other adjustments 57.6 — — — Fair value of plan assets at end of fiscal year $ 4,107.9 $ 1,414.7 $ 4,301.5 $ 774.1 Funded status $ 166.0 $ (87.5 ) $ 69.8 $ (151.1 ) Amounts recognized in consolidated balance sheet: Non-current assets $ 340.4 $ 27.6 $ 247.3 $ 10.5 Other current liability (9.3 ) (0.8 ) (9.9 ) (1.1 ) Accrued pension and other long-term benefits (165.1 ) (114.3 ) (167.6 ) (160.5 ) Over (under) funded status at end of fiscal year $ 166.0 $ (87.5 ) $ 69.8 $ (151.1 ) The following table shows the changes in benefit obligation and plan assets, and the plan’s funded status for the years ended September 30 (in millions): Postretirement Plans 2017 2016 Change in projected benefit obligation U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Benefit obligation at beginning of fiscal year $ 90.7 $ 62.6 $ 109.5 $ 51.6 Service cost 0.1 0.8 1.7 0.6 Interest cost 3.3 4.1 4.5 3.6 Amendments (3.4 ) (1.0 ) (4.0 ) — Actuarial loss (gain) 14.1 0.4 (6.3 ) 5.0 Benefits paid (8.0 ) (2.7 ) (14.1 ) (2.5 ) Business combinations 1.3 2.0 — — Business divestitures — (0.4 ) (0.6 ) — Curtailments — (0.3 ) — — Foreign currency rate changes — 2.6 — 4.3 Benefit obligation at end of fiscal year $ 98.1 $ 68.1 $ 90.7 $ 62.6 Change in plan assets Fair value of plan assets at beginning of fiscal year $ — $ — $ — $ — Employer contributions 8.0 2.7 14.1 2.5 Plan participant contributions — — — — Benefits paid (8.0 ) (2.7 ) (14.1 ) (2.5 ) Fair value of plan assets at end of fiscal year $ — $ — $ — $ — Funded Status $ 98.1 $ 68.1 $ 90.7 $ 62.6 Amounts recognized in the consolidated balance sheet: Other current liability $ (9.8 ) $ (3.0 ) $ (10.4 ) $ (2.9 ) Accrued postretirement and other long-term benefits (88.3 ) (65.1 ) (80.3 ) (59.7 ) Under funded status at end of fiscal year $ (98.1 ) $ (68.1 ) $ (90.7 ) $ (62.6 )
Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year [Table Text Block]	The estimated losses that will be amortized from accumulated other comprehensive loss into net periodic benefit cost in fiscal 2018 are as follows (in millions): Pension Plans U.S. Plans Non-U.S. Plans Actuarial loss $ 12.2 $ 6.2 Prior service cost 4.3 0.1 Total $ 16.5 $ 6.3 The estimated (gains) losses that will be amortized from accumulated other comprehensive loss into net periodic benefit cost in fiscal 2018 are as follows (in millions): Postretirement Plans U.S. Plans Non-U.S. Plans Actuarial (gain) loss $ (0.9 ) $ 0.7 Prior service credit (4.0 ) (0.2 ) Total $ (4.9 ) $ 0.5
Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block]	The pre-tax amounts recognized in other comprehensive (income) loss, including noncontrolling interest, are as follows at September 30 (in millions): Pension Plans 2017 2016 2015 Net actuarial (gain) loss arising during period $ (48.8 ) $ 355.4 $ 85.9 Amortization and settlement recognition of net actuarial loss (57.7 ) (381.6 ) (49.2 ) Prior service cost arising during period 3.4 1.5 26.4 Amortization of prior service cost (4.1 ) (3.9 ) (3.0 ) Net other comprehensive (income) loss recognized $ (107.2 ) $ (28.6 ) $ 60.1 s): Postretirement Plans 2017 2016 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Net actuarial (gain) loss $ (9.1 ) $ 4.2 $ (24.9 ) $ 4.1 Prior service credit (13.9 ) (1.4 ) (14.9 ) (0.4 ) Total accumulated other comprehensive (income) loss $ (23.0 ) $ 2.8 $ (39.8 ) $ 3.7 The pre-tax amounts recognized in other comprehensive loss (income), including noncontrolling interest, are as follows at September 30 (in millions): Postretirement Plans 2017 2016 2015 Net actuarial loss (gain) arising during period $ 14.7 $ (1.4 ) $ (4.4 ) Amortization and settlement recognition of net actuarial gain 1.3 1.9 1.1 Prior service credit arising during period (4.4 ) (3.8 ) (1.4 ) Amortization or curtailment recognition of prior service credit 4.5 2.1 10.5 Net other comprehensive loss (income) recognized $ 16.1 $ (1.2 ) $ 5.8
Schedule of Accumulated and Projected Benefit Obligations [Table Text Block]	The pre-tax amounts in accumulated other comprehensive loss at September 30 not yet recognized as components of net periodic pension cost, including noncontrolling interest, consist of (in millions): Pension Plans 2017 2016 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Net actuarial loss $ 547.3 $ 173.9 $ 633.4 $ 195.8 Prior service cost 27.6 0.4 28.2 0.4 Total accumulated other comprehensive loss $ 574.9 $ 174.3 $ 661.6 $ 196.2 The pre-tax amounts in accumulated other comprehensive loss at September 30 not yet recognized as components of net periodic postretirement cost, including noncontrolling interest, consist of (in millions): Postretirement Plans 2017 2016 U.S. Plans Non-U.S. Plans U.S. Plans Non-U.S. Plans Net actuarial (gain) loss $ (9.1 ) $ 4.2 $ (24.9 ) $ 4.1 Prior service credit (13.9 ) (1.4 ) (14.9 ) (0.4 ) Total accumulated other comprehensive (income) loss $ (23.0 ) $ 2.8 $ (39.8 ) $ 3.7
Schedule of Net Benefit Costs [Table Text Block]	The net periodic postretirement cost recognized in the consolidated statements of operations is comprised of the following for fiscal years ended (in millions): Postretirement Plans 2017 2016 2015 Service cost $ 0.9 $ 2.3 $ 1.0 Interest cost 7.4 8.1 5.4 Amortization of net actuarial gain (1.3 ) (2.0 ) (1.1 ) Amortization of prior service credit (4.5 ) (2.1 ) (2.0 ) Curtailment gain (0.3 ) — (8.5 ) Net postretirement cost (credit) $ 2.2 $ 6.3 $ (5.2 ) The net periodic pension cost recognized in the consolidated statements of operations is comprised of the following for fiscal years ended (in millions): Pension Plans 2017 2016 2015 Service cost $ 45.1 $ 51.4 $ 44.7 Interest cost 197.8 310.3 218.1 Expected return on plan assets (313.1 ) (412.3 ) (292.9 ) Amortization of net actuarial loss 25.4 11.0 29.0 Amortization of prior service cost 4.1 3.9 3.0 Curtailment gain — (1.6 ) — Settlement loss 32.7 370.7 20.2 Special termination benefits 12.5 18.4 9.1 Company defined benefit plan expense 4.5 351.8 31.2 Multiemployer and other plans 4.7 5.8 5.6 Net pension cost $ 9.2 $ 357.6 $ 36.8
Schedule of Health Care Cost Trend Rates [Table Text Block]	The assumed health care cost trend rates used in measuring the APBO are as follows at September 30: 2017 U.S. Plans Health care cost trend rate assumed for next year 6.29 % Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) 4.43 % Year the rate reaches the ultimate trend rate 2037 Non-U.S. Plans Health care cost trend rate assumed for next year 7.27 % Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) 6.16 % Year the rate reaches the ultimate trend rate 2029
Schedule of Expected Benefit Payments [Table Text Block]	Our projected estimated benefit payments (unaudited), which reflect expected future service, as appropriate, are as follows (in millions): Postretirement Plans U.S. Plans Non-U.S. Plans Fiscal 2018 $ 9.8 $ 3.0 Fiscal 2019 $ 8.6 $ 3.1 Fiscal 2020 $ 8.0 $ 3.2 Fiscal 2021 $ 7.6 $ 3.3 Fiscal 2022 $ 7.3 $ 3.3 Fiscal Years 2023 – 2027 $ 32.1 $ 18.3 Our projected estimated benefit payments (unaudited), which reflect expected future service, as appropriate, are as follows (in millions): Pension Plans U.S. Plans Non-U.S. Plans Fiscal 2018 $ 200.5 $ 82.2 Fiscal 2019 $ 206.8 $ 82.6 Fiscal 2020 $ 217.9 $ 81.7 Fiscal 2021 $ 222.6 $ 81.9 Fiscal 2022 $ 213.1 $ 81.9 Fiscal Years 2023 – 2027 $ 1,146.5 $ 408.4
Fair Value, Assets Measured on Recurring Basis [Table Text Block]	The following table summarizes our pension plan assets measured at fair value on a recurring basis (at least annually) as of September 30, 2017 (in millions): Total Quoted Prices Significant Equity securities: U.S. equities (1) $ 136.7 $ 136.6 $ 0.1 Non-U.S. equities (1) 40.0 40.0 — Fixed income securities: U.S. government securities (2) 452.0 — 452.0 Non-U.S. government securities (3) 130.0 — 130.0 U.S. corporate bonds (3) 1,515.4 92.3 1,423.1 Non-U.S. corporate bonds (3) 373.7 51.1 322.6 Mortgage-backed securities (3) 0.1 — 0.1 Other fixed income (4) 311.4 — 311.4 Short-term investments (5) 184.6 184.6 — Benefit plan assets measured in the fair value hierarchy $ 3,143.9 $ 504.6 $ 2,639.3 Assets measured at NAV (6) 2,378.7 Total benefit plan assets $ 5,522.6 The following table summarizes our pension plan assets measured at fair value on a recurring basis (at least annually) as of September 30, 2016 (in millions): Total Quoted Prices Significant Equity securities: U.S. equities (1) $ 192.7 $ 192.7 $ — Non-U.S. equities (1) 74.1 73.5 0.6 Fixed income securities: U.S. government securities (2) 1,271.1 — 1,271.1 Non-U.S. government securities (3) 93.4 5.3 88.1 U.S. corporate bonds (3) 616.9 9.0 607.9 Non-U.S. corporate bonds (3) 255.2 6.4 248.8 Mortgage-backed securities (3) 2.4 — 2.4 Other fixed income (4) 317.5 — 317.5 Short-term investments (5) 302.1 302.1 — Benefit plan assets measured in the fair value hierarchy $ 3,125.4 $ 589.0 $ 2,536.4 Assets measured at NAV (6) 1,950.2 Total benefit plan assets $ 5,075.6 (1) Equity securities are comprised of the following investment types: (i) common stock, (ii) preferred stock and (iii) equity exchange traded funds. Level 1 investments in common and preferred stocks and exchange traded funds are valued using quoted market prices multiplied by the number of shares owned. (2) U.S. government securities include treasury and agency debt. These investments are valued using broker quotes in an active market. (3) The level 1 non-U.S. government securities investment is an exchange traded fund valued using quoted market prices. The level 1 U.S. corporate bonds category is primarily comprised of U.S. dollar denominated investment grade securities and valued using quoted market prices. Level 2 investments are valued utilizing a market approach that includes various valuation techniques and sources such as value generation models, broker quotes in active and non-active markets, benchmark yields and securities, reported trades, issuer spreads, and/or other applicable reference data. (4) Other fixed income is comprised of municipal and asset-backed securities. Investments are valued utilizing a market approach that includes various valuation techniques and sources, such as broker quotes in active and non-active markets, benchmark yields and securities, reported trades, issuer spreads and/or other applicable reference data. (5) Short-term investments are valued at $1.00/unit, which approximates fair value. Amounts are generally invested in interest-bearing accounts. (6) Investments that are measured at NAV (or its equivalent) as a practical expediency have not been classified in the fair value hierarchy.
Schedule Of Multiemployer Plans [Table Text Block]	The following table lists our participation in our multiemployer and other plans that are individually significant for the years ended September 30 (in millions): Pension Fund EIN / Pension Plan Number Pension Act Zone Status FIP / RP Status Pending / Implemented Contributions (1) Surcharge imposed? Expiration CBA 2017 2016 2017 2016 2015 U.S. Multiemployer plans: Pace Industry Union-Management Pension Fund (2) 11-6166763 / 001 Red Red Implemented $ 3.5 $ 3.3 $ 3.3 Yes 6/1/17 to 6/25/23 Other Funds (3) 1.6 1.2 1.7 Total Contributions: $ 5.1 $ 4.5 $ 5.0 (1) Contributions represent the amounts contributed to the plan during the fiscal year. (2) Our contributions for fiscal 2016 and 2015 exceeded 5% of total plan contributions. Although the plan data for fiscal 2017 is not yet available, we would expect to continue to exceed 5% of total plan contributions. (3) Two additional MEPPs in which we participate have been certified in the red zone for critical and declining.
Schedule of Defined Benefit Plans Disclosures [Table Text Block]	The following table summarizes assets measured at fair value based on NAV per share as a practical expedient as of September 30, 2017 and 2016 (in millions): Fair value Redemption Frequency Redemption Notice Period Unfunded Commitments September 30, 2017 Hedge funds (1) $ 64.2 Quarterly Up to 91 days $ — Commingled funds, private equity and private real estate investments, and equity related investments (2) 1,207.6 Monthly Up to 60 days 98.8 Fixed income and fixed income related instruments (3) 1,106.9 Monthly Up to 10 days — $ 2,378.7 $ 98.8 September 30, 2016 Hedge funds (1) $ 265.7 Quarterly Up to 91 days $ — Commingled funds, private equity, private real estate investments, and equity related investments (2) 881.3 Monthly Up to 60 days 123.6 Fixed income and fixed income related instruments (3) 744.1 Monthly Up to 10 days — Other (4) 59.1 Daily Up to 5 days — $ 1,950.2 $ 123.6 (1) Hedge fund investments are primarily made through shares of limited partnerships or similar structures. Hedge funds are typically valued monthly by third-party administrators that have been appointed by the funds’ general partners. Hedge funds have been valued using NAV as a practical expedient. (2) Commingled fund investments are valued at the net asset value per share multiplied by the number of shares held. The determination of net asset value for the commingled funds includes market pricing of the underlying assets as well as broker quotes and other valuation techniques. Commingled funds have been valued using NAV as a practical expedient. We maintain holdings in certain private equity partnerships and private real estate investments for which a liquid secondary market does not exist. The private equity partnerships are commingled investments. Valuation techniques, such as discounted cash flow and market based comparable analyses, are used to determine fair value of the private equity investments. Unobservable inputs used for the discounted cash flow technique include projected future cash flows and the discount rate applied to present value those cash flows. Unobservable inputs used for the market based comparisons technique include EBITDA multiples in other comparable third-party transactions, price to earnings ratios, liquidity, current operating results, as well as input from general partners and other pertinent information. Private equity investments have been valued using NAV as a practical expedient. Private real estate investments are commingled investments. Valuation techniques, such as discounted cash flow and market based comparable analyses, are used to determine fair value of the private equity investments. Unobservable inputs used for the discounted cash flow technique include projected future cash flows and the discount rate applied to present value those cash flows. Unobservable inputs used for the market based comparison technique include a combination of third party appraisals, replacement cost, and comparable market prices. Private real estate investments have been valued using NAV as a practical expedient. Equity related investments are hedged equity investments in a commingled fund that consist primarily of equity indexed investments which are hedged by options and also hold collateral in the form of short term treasury securities. Equity related investments have been valued using NAV as a practical expedient. (3) Fixed income and fixed income related instruments consist of commingled debt funds, which are valued at their net asset value per share multiplied by the number of shares held. The determination of net asset value for the commingled funds includes market pricing of the underlying assets as well as broker quotes and other valuation techniques. Commingled debt funds have been valued using NAV as a practical expedient. (4) Consists of a global multi-asset investment commingled fund with underlying investments that are diversified across multiple asset classes and include global equity, fixed income securities, commodities and derivative contracts. The commingled fund is valued at its net asset value per share multiplied by the number of shares held. The determination of net asset value for the commingled fund includes market pricing of the underlying assets as well as broker quotes and other valuation techniques. The global multi-asset investment commingled fund has been valued using NAV as a practical expedient.

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Sep. 30, 2017
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]	We applied the following weighted average assumptions to estimate the fair value of stock option grants made in the following periods, including the grants issued in connection with the Combination in fiscal 2015: 2016 2015 Expected term in years 7.0 3.9 Expected volatility 38.3 % 21.9 % Risk-free interest rate 1.6 % 2.4 % Dividend yield 4.5 % 1.3 %
Summary of stock option and SAR activity	The table below summarizes the changes in all stock options during the fiscal year ended September 30, 2017 : Stock Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in millions) Outstanding at September 30, 2016 8,065,816 $ 29.73 Exercised (2,074,828 ) 27.38 Expired (57,225 ) 32.61 Forfeited (67,636 ) 31.50 Outstanding at September 30, 2017 5,866,127 $ 30.51 4.6 $ 154.6 Exercisable at September 30, 2017 4,883,459 $ 29.94 4.0 $ 131.5 Vested and expected to vest at September 30, 2017 5,853,074 $ 30.50 4.6 $ 154.2 The table below summarizes the changes in all SARs during the fiscal year ended September 30, 2017 : SARs Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in millions) Outstanding at September 30, 2016 65,971 $ 26.07 Exercised (13,868 ) 28.43 Expired (1,087 ) 31.87 Outstanding at September 30, 2017 51,016 $ 25.30 2.8 $ 1.6 Exercisable at September 30, 2017 51,016 $ 25.30 2.8 $ 1.6
Summary of restricted stock awards - vested, granted and changes	The following table represents a summary of restricted stock shares granted in fiscal 2017 , 2016 and 2015 with terms defined in the applicable grant letters. The shares are not deemed to be issued and carry voting rights until the relevant conditions defined in the award documents have been met, unless otherwise noted. 2017 2016 2015 Shares of restricted stock granted to non-employee directors (1) 26,521 64,155 15,255 Shares of restricted stock granted to employees: Shares granted for attainment of a performance condition at an amount in excess of target (2) 340,319 447,261 801,810 Shares granted with a service condition and a Cash Flow Per Share performance condition at target (3) (4) 507,070 1,211,760 379,519 Shares granted with a service condition and a relative Total Shareholder Return market condition at target (3) 301,980 — — Shares granted with a service condition (5) 309,850 27,370 86,265 Shares granted with a service condition and a performance condition prorated upon the Combination (6) — — 64,323 Share of restricted stock assumed in purchase accounting: Shares granted with a service condition and a performance condition (7) (8) — — 650,685 Shares granted with a service condition (8) 119,373 — 327,005 Total restricted stock granted 1,605,113 1,750,546 2,324,862 (1) Non-employee director grants generally vest over a period of up to one year and are deemed issued on the grant date and have voting and dividend rights. (2) Shares granted in the table above include shares subsequently issued for the level of performance attained in excess of target. Shares issued in fiscal 2017 for the fiscal 2014 Cash Flow to Equity Ratio were at 176.6% of target. Shares issued in fiscal 2016 for the fiscal 2013 Cash Flow to Equity Ratio were at 200% of target. Shares issued in fiscal 2015 for the fiscal 2012 Cash Flow to Equity Ratio were at 200% of target. Shares issued in fiscal 2017, 2016 and 2015 also include shares accelerated for terminated employees primarily as a result of the Combination, which were achieved at between 146.5% and 200% of target. (3) These employee grants vest over approximately three years and have adjustable ranges from 0 - 200% of target subject to the level of performance attained in the respective award agreement. The employee grants with a relative Total Shareholder Return condition were valued using a Monte Carlo simulation, the terms of which are outlined below. (4) Shares granted in fiscal 2015 were reduced by 50,326 shares at target related to the rescission of shares granted to our CEO that were inadvertently granted in excess of plan limits. (5) These shares vest over approximately three to four years. (6) As a result of the Combination, certain target awards granted to employees in fiscal 2015 were prorated with the employee receiving approximately 16.6% of the target award in accordance with the terms in the award document prior to the application of the performance adjustment. The performance period applicable to each award ended upon consummation of the Combination, and the performance goals were determined in accordance with the applicable grant letter to be attained at 146.5% of target. (7) The performance period applicable to each award ended upon consummation of the Combination, and the performance goals were determined in accordance with the applicable grant letter to be attained at between 100% and 168% of target. (8) These shares vest over approximately one to three years. The following table represents a summary of restricted stock vested in fiscal 2017 , 2016 and 2015 (in millions, except shares): 2017 2016 2015 Shares of restricted stock vested 1,112,909 1,589,761 1,725,435 Aggregate fair value of restricted stock vested $ 59.5 $ 57.5 $ 110.4 The table below summarizes the changes in unvested restricted stock during the fiscal year ended September 30, 2017 : Shares/Units Weighted Average Grant Date Fair Value Unvested at September 30, 2016 2,704,904 $ 40.89 Granted 1,605,113 53.79 Vested (1,112,909 ) 48.07 Forfeited (237,659 ) 39.69 Unvested at September 30, 2017 (1) 2,959,449 $ 45.28 (1) Target awards granted with a performance condition, net of subsequent forfeitures, may be increased up to 200% of the target or decreased to zero , subject to the level of performance attained. The awards are reflected in the table at the target award amount of 100% . Based on current facts and assumptions we are forecasting the performance of the grants to be attained at levels that would result in the issuance of approximately 1.4 million additional shares. However, it is possible that the performance attained may vary.

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Sep. 30, 2017
Revenues from External Customers, Segment Income and Long-Lived Assets [Line Items]
Schedule of Revenue from External Customers, Segment Income and Long-Lived Assets, by Geographical Areas [Table Text Block]	The table below reflects financial data of our foreign operations for each of the past three fiscal years (in millions, except percentages): Years Ended September 30, 2017 2016 2015 Foreign net sales to unaffiliated customers $ 2,621.2 $ 2,426.6 $ 1,506.5 Foreign segment income $ 260.1 $ 226.1 $ 171.6 Foreign long-lived assets $ 1,558.3 $ 1,341.5 $ 1,228.0 Foreign operations as a percent of consolidated operations: Foreign net sales to unaffiliated customers 17.6 % 17.1 % 13.5 % Foreign segment income 21.8 % 18.4 % 16.0 % Foreign long-lived assets 17.1 % 14.4 % 13.4 %
Certain operating data for segments	The following table shows selected operating data for our segments (in millions): Years Ended September 30, 2017 2016 2015 Net sales (aggregate): Corrugated Packaging $ 8,408.3 $ 7,868.5 $ 7,516.9 Consumer Packaging 6,452.5 6,388.1 3,740.1 Land and Development 243.8 119.8 45.0 Total $ 15,104.6 $ 14,376.4 $ 11,302.0 Less net sales (intersegment): Corrugated Packaging $ 155.8 $ 136.2 $ 130.6 Consumer Packaging 89.1 68.4 46.6 Total $ 244.9 $ 204.6 $ 177.2 Net sales (unaffiliated customers): Corrugated Packaging $ 8,252.5 $ 7,732.3 $ 7,386.3 Consumer Packaging 6,363.4 6,319.7 3,693.5 Land and Development 243.8 119.8 45.0 Total $ 14,859.7 $ 14,171.8 $ 11,124.8 Segment income: Corrugated Packaging $ 753.9 $ 739.9 $ 806.7 Consumer Packaging 425.8 481.7 267.0 Land and Development 13.8 4.6 (3.4 ) Segment income 1,193.5 1,226.2 1,070.3 Pension risk transfer expense — (370.7 ) — Pension lump sum settlement and retiree medical curtailment, net (32.6 ) — (11.5 ) Land and Development impairment (46.7 ) — — Restructuring and other costs, net (196.7 ) (366.4 ) (140.8 ) Non-allocated expenses (43.5 ) (49.1 ) (58.4 ) Interest expense (277.7 ) (256.7 ) (132.5 ) Gain (loss) on extinguishment of debt 1.8 2.7 (2.6 ) Interest income and other income (expense), net 66.7 58.6 9.7 Gain on sale of HH&B 192.8 — — Income from continuing operations before income taxes $ 857.6 $ 244.6 $ 734.2 Segment income in fiscal 2017 , 2016 and 2015 was reduced by $26.5 million , $8.1 million and $64.7 million , respectively, of expense for inventory stepped-up in purchase accounting, net of related LIFO impact. Corrugated Packaging segment income and Consumer Packaging segment income in fiscal 2017 were reduced by $1.4 million and $25.1 million , respectively. The Corrugated Packaging segment income and Consumer Packaging segment income in fiscal 2016 were reduced by $3.4 million and $4.7 million , respectively. Corrugated Packaging segment income and Consumer Packaging segment income in fiscal 2015 were reduced by $2.2 million and $62.5 million , respectively. The following table shows selected operating data for our segments (in millions): Years Ended September 30, 2017 2016 2015 Identifiable assets: Corrugated Packaging $ 10,537.7 $ 10,046.0 $ 9,467.3 Consumer Packaging 11,877.8 10,122.5 10,175.7 Land and Development 89.8 460.6 545.5 Assets of discontinued operations — — 2,618.5 Assets held for sale 173.6 52.3 10.2 Corporate 2,410.1 2,356.8 2,555.2 Total $ 25,089.0 $ 23,038.2 $ 25,372.4 Goodwill: Corrugated Packaging $ 1,865.7 $ 1,722.5 $ 1,667.5 Consumer Packaging 3,662.6 3,055.6 2,979.6 Total $ 5,528.3 $ 4,778.1 $ 4,647.1 Depreciation and amortization: Corrugated Packaging $ 597.9 $ 576.2 $ 496.6 Consumer Packaging 508.2 498.9 201.8 Land and Development 0.7 1.4 0.2 Discontinued operations — 57.2 22.0 Corporate 9.8 12.8 20.2 Total $ 1,116.6 $ 1,146.5 $ 740.8 Capital expenditures: Corrugated Packaging $ 492.1 $ 490.1 $ 378.4 Consumer Packaging 265.8 244.9 166.1 Discontinued operations — 45.2 28.6 Corporate 20.7 16.5 12.4 Total $ 778.6 $ 796.7 $ 585.5 Investment in unconsolidated entities: Corrugated Packaging $ 321.1 $ 281.2 $ 7.9 Consumer Packaging 24.7 22.2 21.3 Land and Development 14.4 28.6 31.0 Corporate 0.4 (3.1 ) — Total $ 360.6 $ 328.9 $ 60.2 The increase in the Corrugated Packaging segment’s investment in unconsolidated entities in fiscal 2016 was primarily related to the Grupo Gondi investment. The Corporate investment in unconsolidated entities in fiscal 2016 primarily represented an entity that had losses that were guaranteed equally by the partners; this subsidiary has since been sold. The investment in Grupo Gondi that is included in the Corrugated Packaging segment’s investment in unconsolidated entities in fiscal 2017 and 2016 exceeds our proportionate share of the underlying equity in net assets by approximately $76.2 million and $65.3 million , respectively. Approximately $59.2 million and $56.2 million remains amortizable to expense in equity in income of unconsolidated entities over the estimated life of the underlying assets ranging from 10 to 15 years beginning with our investment in fiscal 2016. In fiscal 2017, our equity participation in the Grupo Gondi joint venture increased due to the joint venture entity’s stock redemption from a minority partner. As a result, our equity participation in the joint venture increased to approximately 27.0% . See “ Note 23. Subsequent Events (Unaudited) — Grupo Gondi Investment ” for recent developments.
Changes in carrying amount of goodwill	The changes in the carrying amount of goodwill for the fiscal years ended September 30, 2017 , 2016 and 2015 are as follows (in millions): Corrugated Packaging Consumer Packaging Total Balance as of October 1, 2014 Goodwill $ 1,525.4 $ 443.8 $ 1,969.2 Accumulated impairment losses — (42.8 ) (42.8 ) 1,525.4 401.0 1,926.4 Goodwill acquired 183.3 2,586.5 2,769.8 Purchase price allocation adjustments 2.4 (1.1 ) 1.3 Translation adjustment (43.6 ) (6.8 ) (50.4 ) Balance as of September 30, 2015 Goodwill 1,667.5 3,022.4 4,689.9 Accumulated impairment losses — (42.8 ) (42.8 ) 1,667.5 2,979.6 4,647.1 Goodwill acquired 52.4 8.0 60.4 Goodwill disposed of (24.0 ) — (24.0 ) Purchase price allocation adjustments (4.9 ) 67.6 62.7 Translation adjustment 31.5 0.4 31.9 Balance as of September 30, 2016 Goodwill 1,722.5 3,098.4 4,820.9 Accumulated impairment losses — (42.8 ) (42.8 ) 1,722.5 3,055.6 4,778.1 Goodwill acquired 137.6 907.8 1,045.4 Goodwill disposed of — (329.6 ) (329.6 ) Purchase price allocation adjustments (1.2 ) 9.3 8.1 Translation adjustment 6.8 19.5 26.3 Balance as of September 30, 2017 Goodwill 1,865.7 3,705.4 5,571.1 Accumulated impairment losses — (42.8 ) (42.8 ) $ 1,865.7 $ 3,662.6 $ 5,528.3 The goodwill acquired in fiscal 2017 related to the MPS Acquisition and the Hannapak Acquisition in the Consumer Packaging segment and the U.S. Corrugated Acquisition, the Island Container Acquisition and the Star Pizza Acquisition in the Corrugated Packaging segment. The goodwill disposed of in the Consumer Packaging segment in fiscal 2017 was primarily related to the HH&B Sale. The goodwill acquired in fiscal 2016 related to the SP Fiber Acquisition and the Packaging Acquisition in the Corrugated Packaging and Consumer Packaging segments, respectively. The goodwill disposed of in the Corrugated Packaging segment in fiscal 2016 relates to the disposal of a portion of the reporting unit in connection with the investment in the Grupo Gondi unconsolidated joint venture. The goodwill acquired in fiscal 2015 primarily relates to the Combination. See “ Note 6. Merger, Acquisitions and Investment ”.

Financial Results by Quarter 51

Financial Results by Quarter (Unaudited) (Tables)	12 Months Ended
	Sep. 30, 2017
Financial Results by Quarter (Unaudited) [Abstract]
Schedule of Quarterly Financial Information	Fiscal 2017 First Quarter Second Quarter Third Quarter Fourth Quarter (In millions, except per share data) Net sales $ 3,447.2 $ 3,656.3 $ 3,695.6 $ 4,060.6 Gross profit $ 591.3 $ 675.4 $ 695.5 $ 778.0 Pension lump sum settlement and retiree medical curtailment, net $ — $ 28.7 $ — $ 3.9 Land and Development impairment $ — $ 42.7 $ — $ 4.0 Restructuring and other costs, net $ 81.0 $ 18.3 $ 59.4 $ 38.0 (Loss) gain on extinguishment of debt $ — $ (0.1 ) $ 2.0 $ (0.1 ) Gain on sale of HH&B $ — $ — $ 190.6 $ 2.2 Consolidated net income $ 78.5 $ 98.2 $ 326.6 $ 195.3 Net income attributable to common stockholders $ 80.9 $ 103.1 $ 328.1 $ 196.1 Basic earnings per share attributable to common stockholders $ 0.32 $ 0.40 $ 1.29 $ 0.77 Diluted earnings per share attributable to common stockholders $ 0.32 $ 0.40 $ 1.29 $ 0.76 Fiscal 2016 First Quarter Second Quarter Third Quarter Fourth Quarter (In millions, except per share data) Net sales $ 3,470.9 $ 3,492.7 $ 3,596.5 $ 3,611.7 Gross profit $ 654.7 $ 657.3 $ 727.3 $ 719.3 Pension risk transfer expense $ — $ — $ — $ 370.7 Restructuring and other costs, net $ 162.8 $ 111.1 $ 43.1 $ 49.4 Gain on extinguishment of debt $ — $ — $ — $ 2.7 Income (loss) from continuing operations $ 30.4 $ 58.4 $ 152.4 $ (86.4 ) (Loss) income from discontinued operations, net of tax $ (482.1 ) $ 1.4 $ (58.7 ) $ (5.3 ) Consolidated net (loss) income $ (451.7 ) $ 59.8 $ 93.7 $ (91.7 ) Net (loss) income attributable to common stockholders $ (453.5 ) $ 56.9 $ 92.3 $ (92.0 ) Basic earnings (loss) per share from continuing operations $ 0.12 $ 0.22 $ 0.60 $ (0.34 ) Diluted earnings (loss) per share from continuing operations $ 0.12 $ 0.22 $ 0.59 $ (0.34 ) Basic (loss) earnings per share attributable to common stockholders $ (1.76 ) $ 0.22 $ 0.37 $ (0.37 ) Diluted (loss) earnings per share attributable to common stockholders $ (1.73 ) $ 0.22 $ 0.36 $ (0.37 )

Description of Business and S52

Description of Business and Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Description of Business and Summary of Significant Accounting Policies [Line Items]
Gain on sale of HH&B	$ 2.2	$ 190.6	$ 0	$ 0	$ 192.8	$ 0	$ 0
Percentage of FIFO Inventory	32.00%				32.00%	35.00%
Interest Costs, Capitalized During Period					$ 7	$ 7.6	4
Percentage of our mill assets as measured at cost with a life of 25 years or less					90.00%
Finite-Lived Intangible Assets, Useful Life					16 years 7 months
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period					3 years
Asset Retirement Obligation	$ 70.5				$ 70.5	78.9
Foreign Currency Transaction Gain, after Tax					4.3	(6.5)	2.9
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of fiscal year				$ 36.5	36.5	29.5	25.1
Reduction in sales and charges to costs and expenses					215.6	200.8	166.6
Reductions					(206.3)	(193.8)	(162.2)
Balance at end of fiscal year	45.8				$ 45.8	$ 36.5	$ 29.5
Minimum [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Accounts Receivable, Approximate Range Receivables Due, Days					30 days
Finite-Lived Intangible Assets, Useful Life					1 year
Minimum [Member] | Building and Building Improvements [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life					15 years
Minimum [Member] | Machinery and Equipment [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life					3 years
Minimum [Member] | Transportation Equipment [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life					3 years
Minimum [Member] | Leasehold Improvements [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life					3 years
Maximum [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Accounts Receivable, Approximate Range Receivables Due, Days					60 days
Finite-Lived Intangible Assets, Useful Life					40 years
Maximum [Member] | Building and Building Improvements [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life					40 years
Maximum [Member] | Machinery and Equipment [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life					25 years
Maximum [Member] | Transportation Equipment [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life					8 years
Maximum [Member] | Machinery and Equipment, Mills [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life					44 years
Maximum [Member] | Cost of Our Mill Machinery and Equipment with a Life of 25 Years or Less
Description of Business and Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life					25 years
Maximum [Member] | Leasehold Improvements [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life					10 years
Restricted Stock, Non-Employee Directors [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period					1 year
Foreign Exchange Contract [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Derivative, Notional Amount	$ 47.8				$ 47.8

Earnings per Share (Details)

Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016		Sep. 30, 2015		May 27, 2011
Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income (loss) from continuing operations					$ (86.4)	$ 152.4	$ 58.4	$ 30.4	$ 698.6	$ 154.8		$ 501.2
Less: Net loss (income) from continuing operations attributable to noncontrolling interest									9.6	(2.1)		(3.3)
Income available to common stockholders, before discontinued operations									708.2	152.7		497.9
Less: Distributed and undistributed income available to participating securities									(0.1)	0		0
Distributed and undistributed income attributable to common stockholders, before discontinued operations									708.1	152.7		497.9
(Loss) income from discontinued operations (1)									0	(549)	[1]	9.2	[1]
Net income (loss) attributable to common stockholders									708.1	(396.3)		507.1
Less: Distributed and undistributed income available to participating securities									(0.1)	0		0
Distributed and undistributed income attributable to common stockholders, before discontinued operations									708.1	152.7		497.9
Net income (loss) attributable to common stockholders									$ 708.1	$ (396.3)		$ 507.1
Basic weighted average shares outstanding									252.2	254		170.6
Basic earnings per share from continuing operations					$ (0.34)	$ 0.60	$ 0.22	$ 0.12	$ 2.81	$ 0.60		$ 2.92
Basic (loss) earnings per share from discontinued operations									0	(2.16)		0.05
Basic earnings (loss) per share attributable to common stockholders	$ 0.77	$ 1.29	$ 0.40	$ 0.32	(0.37)	0.37	0.22	(1.76)	$ 2.81	$ (1.56)		$ 2.97
Effect of dilutive stock options and non-participating securities									3.5	3.9		2.7
Diluted weighted average shares outstanding									255.7	257.9		173.3
Diluted earnings per share from continuing operations					(0.34)	0.59	0.22	0.12	$ 2.77	$ 0.59		$ 2.87
Diluted (loss) earnings per share from discontinued operations									0	(2.13)		0.06
Diluted earnings (loss) per share attributable to common stockholders	$ 0.76	$ 1.29	$ 0.40	$ 0.32	$ (0.37)	$ 0.36	$ 0.22	$ (1.73)	$ 2.77	$ (1.54)		$ 2.93
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Noncontrolling Interest										$ 4.3		$ 1.4
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									0.7	1.6		0.4
Smurfit Stone [Member]
Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance	0.2				0.3				0.2	0.3				1.4
[1]	Net of income attributable to noncontrolling interests of discontinued operations of $4.3 million and $1.4 million for the fiscal years ended September 30, 2016 and 2015.

Schedule of Accumulated Other C

Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of fiscal year	[1]	$ (626.4)		$ (780.2)
Other comprehensive (loss) income before reclassifications	[1]	104.3		(112.7)
Amounts reclassified from accumulated other comprehensive loss	[1],[2]	35.1		258.6
Net current period other comprehensive income		169.1	[1]	145.9	[1]	$ (284.9)
Separation of Business	[1]	29.7		7.9
Balance at end of fiscal year	[1]	(457.3)		(626.4)		(780.2)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of fiscal year	[1]	(0.2)		(1.4)
Other comprehensive (loss) income before reclassifications	[1]	0		(0.4)
Amounts reclassified from accumulated other comprehensive loss	[1],[2]	(0.5)		1.2
Net current period other comprehensive income	[1]	(0.5)		0.8
Separation of Business	[1]	0		0.4
Balance at end of fiscal year	[1]	(0.7)		(0.2)		(1.4)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of fiscal year	[1]	(523.8)		(540.7)
Other comprehensive (loss) income before reclassifications	[1]	22.8		(222.2)
Amounts reclassified from accumulated other comprehensive loss	[1],[2]	35.6		237.2
Net current period other comprehensive income	[1]	61.3		15
Separation of Business	[1]	2.9		1.9
Balance at end of fiscal year	[1]	(462.5)		(523.8)		(540.7)
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of fiscal year	[1]	(102.4)		(238.1)
Other comprehensive (loss) income before reclassifications	[1]	80.8		109.9
Amounts reclassified from accumulated other comprehensive loss	[1],[2]	0		20.2
Net current period other comprehensive income	[1]	107.6		130.1
Separation of Business	[1]	26.8		5.6
Balance at end of fiscal year	[1]	5.2		(102.4)		(238.1)
Accumulated Net Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of fiscal year	[1]	0		0
Other comprehensive (loss) income before reclassifications	[1]	0.7		0
Amounts reclassified from accumulated other comprehensive loss	[1],[2]	0		0
Net current period other comprehensive income	[1]	0.7		0
Separation of Business	[1]	0		0
Balance at end of fiscal year	[1]	$ 0.7		$ 0		$ 0
[1]	All amounts are net of tax and noncontrolling interest.
[2]	Amounts reclasssified from accumulated other comprehensive loss for defined benefit pension and postretirement plans in fiscal 2016 includes the pension risk transfer expense, net of tax.

Reclassification out of Accumul

Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016		Sep. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss		$ (56.4)	$ (379.7)		$ (48.1)
Amortization of net actuarial loss, Tax		20.4	143.2	[1]	17.8
Amortization and settlement recognition of net actuarial loss, included in pension and postretirement cost (1)		(36)	(236.5)	[1],[2]	(30.3)
Amortization of prior service (cost) credit		0.4	(1.8)		7.5
Amortization of prior service credit (cost), Tax		(0.2)	0.7		(2.9)
Amortization and curtailment recognition of prior service (credit) cost, included in pension and postretirement cost		0.2	(1.1)		4.6
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Sale of HH&B, before Tax		(4.2)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Sale of HH&B, Tax		1.3
Sale of HH&B		(2.9)	0		0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale of HH&B, before Tax		26.8
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale of HH&B, Tax		0
Sale of HH&B		26.8	0		0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax			20.2
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Tax			0
Reclassification adjustment of net loss on foreign currency translation included in earnings		0	20.2		0
Other Comprehensive Income (Loss), Foreign Currency Translation Gain (Loss), before Tax		80.7	109.8		(242)
Reclassification adjustment of net loss on cash flow hedges included in earnings, Pre-Tax Amount		(0.8)	1.9		0.7
Reclassification adjustment of net loss on cash flow hedges included in earnings, Tax		0.3	(0.7)		(0.3)
Reclassification adjustment of net (gain) loss on cash flow hedges included in earnings		(0.5)	1.2		$ 0.4
Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss	[3],[4],[5]	(56.3)	(379.4)
Amortization of net actuarial loss, Tax	[3],[4],[5]	20.4	143.2
Amortization and settlement recognition of net actuarial loss, included in pension and postretirement cost (1)	[3],[4],[5]	(35.9)	(236.2)
Amortization of prior service (cost) credit	[3],[5]	0.5	(1.7)
Amortization of prior service credit (cost), Tax	[3],[5]	(0.2)	0.7
Amortization and curtailment recognition of prior service (credit) cost, included in pension and postretirement cost	[3],[5]	0.3	(1)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Sale of HH&B, before Tax	[3],[6]	(4.2)	0
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Sale of HH&B, Tax	[3],[6]	1.3	0
Sale of HH&B	[3],[6]	(2.9)	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	[3]	(60)	(381.1)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	[3]	21.5	143.9
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	[3]	(38.5)	(237.2)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale of HH&B, before Tax	[3],[6]	(26.8)	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale of HH&B, Tax	[3],[6]	0	0
Sale of HH&B	[3],[6]	(26.8)	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax	[3],[7]	0	(20.2)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Tax	[3],[7]	0	0
Reclassification adjustment of net loss on foreign currency translation included in earnings	[3],[7]	0	(20.2)
Other Comprehensive Income (Loss), Foreign Currency Translation Gain (Loss), before Tax	[3]	(26.8)	(20.2)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	[3]	0	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	[3]	(26.8)	(20.2)
Reclassification adjustment of net loss on cash flow hedges included in earnings, Pre-Tax Amount	[3]	0.8	(1.9)
Reclassification adjustment of net loss on cash flow hedges included in earnings, Tax	[3]	(0.3)	0.7
Reclassification adjustment of net (gain) loss on cash flow hedges included in earnings	[3]	0.5	(1.2)
Total Reclassifications From Other Comprehensive Income Before Tax	[3]	(86)	(403.2)
Total Reclassifications From Other Comprehensive Income Tax Portion	[3]	21.2	144.6
Total Reclassifications From Other Comprehensive Income Net Of Tax	[3]	(64.8)	(258.6)
Commodity Contract [Member] | Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustment of net loss on cash flow hedges included in earnings, Pre-Tax Amount	[3],[8]	0	(1.5)
Reclassification adjustment of net loss on cash flow hedges included in earnings, Tax	[3],[8]	0	0.5
Reclassification adjustment of net (gain) loss on cash flow hedges included in earnings	[3],[8]	0	(1)
Foreign Exchange Contract [Member] | Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification adjustment of net loss on cash flow hedges included in earnings, Pre-Tax Amount	[3],[9]	0.8	(0.4)
Reclassification adjustment of net loss on cash flow hedges included in earnings, Tax	[3],[9]	(0.3)	0.2
Reclassification adjustment of net (gain) loss on cash flow hedges included in earnings	[3],[9]	$ 0.5	$ (0.2)
[1]	Includes pension risk transfer expense.
[2]	Fiscal 2016 includes pension risk transfer expense, net of tax.
[3]	Amounts in parentheses indicate charges to earnings. Amounts pertaining to noncontrolling interests are excluded.
[4]	Fiscal 2016 includes pension risk transfer expense.
[5]	These accumulated other comprehensive income components are included in the computation of net periodic pension cost. See “Note 15. Retirement Plans” for additional details.
[6]	Included in gain on sale of HH&B.
[7]	These accumulated other comprehensive income components are included in interest income and other income (expense), net.
[8]	These accumulated other comprehensive income components are included in cost of goods sold.
[9]	These accumulated other comprehensive income components are included in net sales.

Other Comprehensive Income (L56

Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2015
Comprehensive Income
Other Comprehensive Income (Loss), Foreign Currency Translation Gain (Loss), before Tax	$ 80.7		$ 109.8		$ (242)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale of HH&B, before Tax	26.8
Net deferred loss on cash flow hedges, Pre-Tax Amount			(0.7)		(2.6)
Reclassification adjustment of net loss on cash flow hedges included in earnings, Pre-Tax Amount	(0.8)		1.9		0.7
Net actuarial gain (loss) arising during period, Pre-Tax Amount	34.1		(354)		(81.5)
Amortization of net actuarial loss	56.4		379.7		48.1
Prior service (cost) credit arising during period, Pre-Tax Amount	1		2.3		(25)
Amortization of prior service cost (credit), Pre-Tax Amount	(0.4)		1.8		(7.5)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Sale of HH&B, before Tax	4.2
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax			20.2
Consolidated other comprehensive income (loss), Pre-Tax Amount	202.7		161		(309.8)
Less: Other comprehensive (income) loss attributable to noncontrolling interests, Pre-Tax Amount	(0.2)		0.7		0.6
Other comprehensive income (loss) attributable to common stockholders, Pre-Tax Amount	202.5		161.7		(309.2)
Foreign currency translation (loss) gain, Tax	0		0		0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale of HH&B, Tax	0
Net deferred loss on cash flow hedges, Tax			0.3		1
Reclassification adjustment of net loss on cash flow hedges included in earnings, Tax	0.3		(0.7)		(0.3)
Net actuarial gain (loss) arising during period, Tax	(11.9)		129.4		28.9
Amortization of net actuarial loss, Tax	(20.4)		(143.2)	[1]	(17.8)
Other Comprehensive Income (Loss), Pension and Other Postretirement Plans, Net Prior Service (Cost) Credit Arising During Period, Tax	(0.3)		(0.9)		9.6
Amortization of prior service cost (credit), Tax	0.2		(0.7)		2.9
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Sale of HH&B, Tax	(1.3)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Tax			0
Consolidated other comprehensive income (loss), Tax	(33.4)		(15.8)		24.3
Less: Other comprehensive income (loss) attributable to noncontrolling interests, Tax	0		0		0
Other comprehensive income (loss) attributable to common stockholders, Tax	(33.4)		(15.8)		24.3
Foreign currency translation gain (loss), Net of Tax Amount	80.7		109.8		(242)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale of HH&B, Net of Tax	26.8		0		0
Net deferred loss on cash flow hedges, Net of Tax Amount	0		(0.4)		(1.6)
Reclassification adjustment of net loss on cash flow hedges included in earnings, Net of Tax Amount	(0.5)		1.2		0.4
Net actuarial gain (loss) arising during period, Net of Tax Amount	22.2		(224.6)		(52.6)
Amortization of net actuarial loss, included in pension cost, Net of Tax Amount	36		236.5	[1],[2]	30.3
Prior service credit (cost) arising during period, Net of Tax Amount	0.7		1.4		(15.4)
Amortization of prior service cost (credit), Net of Tax Amount	(0.2)		1.1		(4.6)
Unrealized gain on available for sale security	0.7		0		0
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	0
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	0.7
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Sale of HH&B, Net of Tax	2.9		0		0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	0		20.2		0
Consolidated other comprehensive income (loss)	169.3		145.2		(285.5)
Less: Other comprehensive (income) loss attributable to noncontrolling interests, Net of Tax Amount	(0.2)		0.7		0.6
Other comprehensive income (loss) attributable to common stockholders	$ 169.1	[3]	$ 145.9	[3]	$ (284.9)
[1]	Includes pension risk transfer expense.
[2]	Fiscal 2016 includes pension risk transfer expense, net of tax.
[3]	All amounts are net of tax and noncontrolling interest.

Inventories (Details)

Inventories (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Inventories [Abstract]
Finished goods and work in process	$ 905	$ 800.6
Raw materials	614.2	535.7
Supplies and spare parts	360.7	335.7
Inventories at FIFO cost	1,879.9	1,672
LIFO reserve	(82.6)	(33.8)
Net inventories	$ 1,797.3	$ 1,638.2

Property, Plant and Equipment58

Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Property, plant and equipment at cost:
Land and buildings	$ 2,034.3	$ 2,307.9
Machinery and equipment	11,349.7	10,672.9
Forestlands and mineral rights	208.3	201.1
Transportation equipment	30.7	27.6
Leasehold improvements	59.5	62.4
Property, plant and equipment, gross	13,682.5	13,271.9
Less: accumulated depreciation and amortization	(4,564.2)	(3,977.6)
Property, plant and equipment, net	9,118.3	9,294.3
Depreciation	$ 855.9	$ 848.9	$ 578.4

Acquisitions (Details)

Acquisitions (Details) $ / shares in Units, shares in Millions, $ in Millions

Aug. 01, 2017USD ($)

Jul. 17, 2017USD ($)T

Jun. 09, 2017USD ($)sharesT

Jun. 06, 2017USD ($)$ / sharesT

Mar. 13, 2017USD ($)

Apr. 01, 2016USD ($)

Jan. 19, 2016USD ($)

Oct. 01, 2015USD ($)

Jul. 01, 2015USD ($)$ / sharesshares

Sep. 30, 2017USD ($)

Jun. 30, 2017USD ($)

Mar. 31, 2017USD ($)

Dec. 31, 2016USD ($)

Sep. 30, 2016USD ($)

Jun. 30, 2016USD ($)

Mar. 31, 2016USD ($)

Dec. 31, 2015USD ($)

Sep. 30, 2015USD ($)

Sep. 30, 2017USD ($)

Sep. 30, 2016USD ($)

Sep. 30, 2015USD ($)

Jul. 01, 2016USD ($)

Business Acquisition [Line Items]

Net sales

$ 4,060.6

$ 3,695.6

$ 3,656.3

$ 3,447.2

$ 3,611.7

$ 3,596.5

$ 3,492.7

$ 3,470.9

$ 14,859.7

$ 14,171.8

$ 11,124.8

Stock options assumed

1.9

0

$ 210.9

1.9

0

210.9

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Goodwill

5,528.3

4,778.1

5,528.3

4,778.1

Total assets acquired

3,342.4

580.7

16,001.1

$ 3,342.4

580.7

16,001.1

Finite-Lived Intangible Assets, Useful Life

16 years 7 months

Gross Carrying Amount

4,227

3,287.4

$ 4,227

3,287.4

Business Acquisition, Pro Forma Information [Abstract]

Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual

1,067.1

Net income (loss) attributable to common stockholders

196.1

$ 328.1

$ 103.1

$ 80.9

(92)

92.3

$ 56.9

$ (453.5)

708.2

(396.3)

507.1

Equity Method Investments

360.6

328.9

$ 60.2

360.6

328.9

60.2

Recategorization of Certain Restructuring and Related Costs from Integration Costs

$ 17.4

42.6

48.2

Pro Forma [Member]

Business Acquisition [Line Items]

Net sales

14,347

Business Acquisition, Pro Forma Information [Abstract]

Net income (loss) attributable to common stockholders

666.3

Customer Relationships [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

16 years 8 months

Gross Carrying Amount

4,046.2

3,094.4

$ 4,046.2

3,094.4

Favorable Contracts [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

9 years 7 months

Gross Carrying Amount

48.2

48.9

$ 48.2

48.9

Noncompete Agreements [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

2 years

Gross Carrying Amount

$ 2.5

$ 0.2

$ 2.5

$ 0.2

Minimum [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

1 year

Maximum [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

40 years

Grupo Gondi Investment [Member]

Business Acquisition [Line Items]

Payments to Acquire Interest in Joint Venture

$ 175

Acquisition date

Apr. 1, 2016

Business Acquisition, Pro Forma Information [Abstract]

Equity Method Investment, Ownership Percentage

25.00%

Equity Method Investments

$ 300

Pre-Tax Non-Cash Gain in Connection with Investment in Joint Venture

$ 12.1

Packaging Acquisition [Member]

Business Acquisition [Line Items]

Business Acquisition, Cost of Acquired Entity, Purchase Price Net of Cash Acquired

$ 94.1

Collection of Escrow Receivable in Business Combination

$ 3.5

Business Acquisition, Purchase Price Allocation, Notes Payable and LT Debt

$ 1.3

Acquisition date

Jan. 19, 2016

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Cash and cash equivalents

$ 1.7

Property, plant, and equipment

55

Goodwill

9.3

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities

25.8

Packaging Acquisition [Member] | Customer Relationships [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles

$ 10.5

Packaging Acquisition [Member] | Minimum [Member] | Customer Relationships [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

9 years

Packaging Acquisition [Member] | Maximum [Member] | Customer Relationships [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

15 years

SP Fiber [Member]

Business Acquisition [Line Items]

Business Acquisition, Cost of Acquired Entity, Purchase Price Net of Cash Acquired

$ 278.8

Payment for Debt Owed by GPS

36.5

Business Acquisition, Purchase Price Allocation, Notes Payable and LT Debt

$ 13.7

Acquisition date

Oct. 1, 2015

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Cash and cash equivalents

$ 9.2

Property, plant, and equipment

324.8

Goodwill

57.3

Total liabilities and noncontrolling interest assumed

$ 150.3

Percent Ownership in GPS

48.00%

SP Fiber [Member] | Customer Relationships [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

20 years

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles

$ 13.5

Star Pizza Acquisition [Member]

Business Acquisition [Line Items]

Business Acquisition, Cost of Acquired Entity, Purchase Price Net of Cash Acquired

$ 34.6

Business Acquisition, Working Capital Settlement

$ 0.7

Acquisition date

Mar. 13, 2017

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Goodwill

$ 2.2

Star Pizza Acquisition [Member] | Customer Relationships [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

10 years

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles

$ 24.8

U.S. Corrugated [Member]

Business Acquisition [Line Items]

Business Combination, Consideration Transferred, Including Equity Interest in Acquiree Held Prior to Combination

$ 193.7

Acquisition date

Jun. 9, 2017

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Cash and cash equivalents

$ 1.4

Property, plant, and equipment

30

Goodwill

108.2

Business Acquisition, Estimated Working Capital Settlement

3.4

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities

$ 53.2

Business Acquisition, Pro Forma Information [Abstract]

Increase in Containerboard Tons Due to the Vertical Integration of our Corrugated Packaging Segment | T

105,000

Increase in Containerboard Tons Due to Long-term Supply Contract | T

50,000

Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares

2.4

Business Combination, Consideration Transferred, Equity Interests Issued and Issuable

$ 136.1

U.S. Corrugated [Member] | Customer Relationships [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

7 years 6 months

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles

$ 77.8

MeadWestvaco [Member]

Business Acquisition [Line Items]

Business Combination, Consideration Transferred, Including Equity Interest in Acquiree Held Prior to Combination

$ 8,286.7

Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares

130.4

Payments for Repurchase of Common Stock

$ 667.8

Common Stock Par Value Per Share of MeadWestvaco | $ / shares

$ 0.01

Ratio of MeadWestvaco Shares to WestRock Shares

78.00%

Business Acquisition, Equity Interest Issued or Issuable, Number of Shares Issued to MeadWestvaco Stockholders | shares

131.2

Stock options assumed

$ 210.9

Acquisition date

Jul. 1, 2015

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

18 years 9 months

Unfavorable Contracts

$ 38.5

Unfavorable Contracts, Useful Life, Minimum

1 year

Unfavorable Contracts, Useful Life, Maximum

9 years

Fair value step-up

$ 364.5

Adjustment to Unamortized Fair Market Value Step-Up

$ 18.3

Gross Carrying Amount

$ 2,994.2

Business Acquisition, Pro Forma Information [Abstract]

Business Combination, Pro Forma Information, Nonrecurring Expense, Inventory Step Up

71.6

Business Combination, Pro Forma Information, Nonrecurring Expense, Acquisition Related Costs

126.7

Business Combination, Pro Forma Information, Nonrecurring Expense, Loss on Extinguishment of Debt

2.6

Business Combination, Pro Forma Information, Integration Related Costs

$ 75.5

Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares

131.2

Business Combination, Consideration Transferred, Equity Interests Issued and Issuable

$ 8,075.8

MeadWestvaco [Member] | Customer Relationships [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

19 years 2 months

Gross Carrying Amount

$ 2,881.7

MeadWestvaco [Member] | Favorable Contracts [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

8 years 2 months

Gross Carrying Amount

$ 2.4

MeadWestvaco [Member] | Patents [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

9 years 10 months

Gross Carrying Amount

$ 57.2

MeadWestvaco [Member] | Trademarks and Tradenames [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

4 years 6 months

Gross Carrying Amount

$ 52.9

MeadWestvaco [Member] | Minimum [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

1 year

Adjustment to Fair Value Debt Assumed in Business Combination, Amortization Period

1 year

MeadWestvaco [Member] | Maximum [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

20 years

Adjustment to Fair Value Debt Assumed in Business Combination, Amortization Period

32 years

MeadWestvaco [Member] | Amounts Recognized as of Acquisition Date (as adjusted) [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Cash and cash equivalents

[1]

$ 265.7

Current assets, net of cash received

[1]

1,858.3

Property, plant, and equipment

[1]

4,010.8

Prepaid pension asset

[1]

1,397.9

Goodwill

[1]

3,862

Intangible assets

[1]

2,994.2

Restricted assets held by special purpose entities

[1]

1,302

Other long-term assets

[1]

381.8

Total assets acquired

[1]

16,072.7

Current portion of debt

[1]

137.1

Current liabilities

[1]

1,053.8

Long-term debt due after one year

[1]

2,108.9

Non-recourse liabilities held by special purpose entities

[1]

1,181

Accrued pension and other long-term benefits

[1]

235.1

Deferred income tax liabilities

[1]

2,355.7

Other long-term liabilities

[1]

555.1

Noncontrolling interest

[1]

159.3

Total liabilities and noncontrolling interest assumed

[1]

7,786

Net assets acquired

[1],[2]

8,286.7

MeadWestvaco [Member] | Measurement Period Adjustments [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Cash and cash equivalents

[3]

0

Current assets, net of cash received

[3]

(0.5)

Property, plant, and equipment

[3]

19.3

Prepaid pension asset

[3]

(9.9)

Goodwill

[3]

44.7

Intangible assets

[3]

0

Restricted assets held by special purpose entities

[3]

0

Other long-term assets

[3]

18

Total assets acquired

[3]

71.6

Current portion of debt

[3]

74.8

Current liabilities

[3]

(45.6)

Long-term debt due after one year

[3]

18.3

Non-recourse liabilities held by special purpose entities

[3]

0

Accrued pension and other long-term benefits

[3]

0

Deferred income tax liabilities

[3]

(11)

Other long-term liabilities

[3]

35.1

Noncontrolling interest

[3]

0

Total liabilities and noncontrolling interest assumed

[3]

71.6

Net assets acquired

[2],[3]

$ 0

MeadWestvaco [Member] | Amounts Recognized As of Acquisition Date [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Cash and cash equivalents

$ 265.7

Current assets, net of cash received

1,858.8

Property, plant, and equipment

3,991.5

Prepaid pension asset

1,407.8

Goodwill

3,817.3

Intangible assets

2,994.2

Restricted assets held by special purpose entities

1,302

Other long-term assets

363.8

Total assets acquired

16,001.1

Current portion of debt

62.3

Current liabilities

1,099.4

Long-term debt due after one year

2,090.6

Non-recourse liabilities held by special purpose entities

1,181

Accrued pension and other long-term benefits

235.1

Deferred income tax liabilities

2,366.7

Other long-term liabilities

520

Noncontrolling interest

159.3

Total liabilities and noncontrolling interest assumed

7,714.4

Net assets acquired

[2]

$ 8,286.7

MPS [Member]

Business Acquisition [Line Items]

Expected Percentage of Increased Paperboard Consumption Supplied by Company, Low End of Range

35.00%

Expected Percentage of Increased Paperboard Consumption Supplied by Company, High End of Range

45.00%

Business Acquisition, Share Price | $ / shares

$ 18

Expected Integration of Paperboard Into Consumer Packaging Segment | T

225,000

Business Acquisition, Cost of Acquired Entity, Purchase Price Net of Cash Acquired

$ 1,351.1

Business Acquisition, Purchase Price Allocation, Notes Payable and LT Debt

929.1

Fair value of share-based awards issued in business combinations

$ 1.9

Acquisition date

Jun. 6, 2017

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Cash and cash equivalents

$ 47.5

Property, plant, and equipment

486.3

Goodwill

887.7

Total liabilities and noncontrolling interest assumed

$ 1,554.7

Finite-Lived Intangible Assets, Useful Life

14 years 5 months

Gross Carrying Amount

$ 1,017.6

MPS [Member] | Customer Relationships [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

14 years 7 months

Gross Carrying Amount

$ 999.9

MPS [Member] | Trademarks and Tradenames [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

3 years

Gross Carrying Amount

$ 15.2

MPS [Member] | Photo Library [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

10 years

Gross Carrying Amount

$ 2.5

MPS [Member] | Minimum [Member] | Customer Relationships [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

13 years

MPS [Member] | Maximum [Member] | Customer Relationships [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

16 years

Island Container [Member]

Business Acquisition [Line Items]

Expected Integration of Containerboard Into Corrugated Packaging Segment | T

80,000

Business Acquisition, Cost of Acquired Entity, Purchase Price Net of Cash Acquired

$ 84.7

Business Acquisition, Estimated Unpaid Working Capital Settlement

$ 1.2

Acquisition date

Jul. 17, 2017

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Property, plant, and equipment

$ 5.4

Goodwill

27.2

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities

$ 1.2

Island Container [Member] | Customer Relationships [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

8 years 6 months

Gross Carrying Amount

$ 43

Hannapak [Member]

Business Acquisition [Line Items]

Business Acquisition, Cost of Acquired Entity, Purchase Price Net of Cash Acquired

$ 59.4

Acquisition date

Aug. 1, 2017

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Cash and cash equivalents

$ 0.6

Property, plant, and equipment

13.9

Goodwill

20.1

Business Acquisition, Estimated Working Capital Settlement

2.4

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities

$ 7.1

Hannapak [Member] | Customer Relationships [Member]

Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract]

Finite-Lived Intangible Assets, Useful Life

13 years

Gross Carrying Amount

$ 14.5

[1]

The measurement period adjustments were due primarily to refinements to third party appraisals and carrying amounts of certain assets and liabilities as well as adjustments to certain tax accounts based on, among other things, adjustments to deferred tax liabilities, including any appraisal adjustments, analysis of the tax basis of acquired assets and liabilities, other tax adjustments and the classification of supplier financing arrangements. The net impact of the measurement period adjustments resulted in a net increase to goodwill.

[2]

The net assets acquired include the Specialty Chemicals business, which was separated from WestRock on May 15, 2016. See “Note 7. Discontinued Operations” for additional information.

[3]

The measurement period adjustments recorded in fiscal 2016 did not have a significant impact on our consolidated statements of operations for fiscal 2016 or 2015. In addition, these adjustments did not have a significant impact on our consolidated balance sheet as of September 30, 2015. Therefore, we have recorded the cumulative impact in fiscal 2016 and have not retrospectively adjusted the comparative 2015 financial information presented herein.

Discontinued Operations (Detail

Discontinued Operations (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	May 15, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016
Long-term Debt				$ 6,554.8	$ 5,789.2
Specialty Chemicals Business [Member] | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member]
Goodwill, Impairment Loss			$ 478.3
Borrowing in Contemplation of Separation of Business	$ 500
Trust Funded By Company and Assumed by Ingevity to Secure the Principal Payment of Capital Lease Upon Maturity	68.9
Long-Term Asset for the Estimated Fair Value of Principal and Interest Payments on Capital Lease Obligation Assumed By Ingevity	108.2
Capital Lease Obligations [Member] | Secured Debt [Member]
Long-term Debt				$ 177	$ 184.4
Capital Lease Obligations [Member] | Secured Debt [Member] | Specialty Chemicals Business [Member] | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member]
Long-term Debt	$ 80
Debt Instrument, Interest Rate, Effective Percentage	7.67%
Customer Lists [Member] | Specialty Chemicals Business [Member] | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member]
Impairment of Intangible Assets (Excluding Goodwill)		$ 101.1

Discontinued Operations Discont

Discontinued Operations Discontinued Operations (Income Statement Disclosures) (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income tax benefit (expense)					$ 0	$ 32.3	$ (17.5)
(Loss) income from discontinued operations (net of income tax benefit (expense) of $0, $32.3 and $(17.5)	$ (5.3)	$ (58.7)	$ 1.4	$ (482.1)	$ 0	(544.7)	10.6
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member] | Specialty Chemicals Business [Member]
Net sales						533.7	256.5
Cost of goods sold						387.5	184
Gross profit						146.2	72.5
Selling, general and administrative, excluding intangible amortization						65.6	27.4
Selling, general and administrative intangible amortization						28.8	11.5
Restructuring and other costs, net						49.5	6.6
Impairment of Specialty Chemicals goodwill and intangibles						579.4	0
Operating (loss) profit						(577.1)	27
Interest income (expense) and other income (expense), net						0.1	1.1
(Loss) income from discontinued operations before income taxes						(577)	28.1
Income tax benefit (expense)						32.3	(17.5)
(Loss) income from discontinued operations (net of income tax benefit (expense) of $0, $32.3 and $(17.5)						(544.7)	$ 10.6
Costs Associated with the Closure of Brazil Facility and Other Severance and Stock-Based Compensation Expenses						$ 10

Discontinued Operations Disco62

Discontinued Operations Discontinued Operations (Depreciation, Amortization and Capital Expenditures) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Impairment of Specialty Chemicals goodwill and intangibles	$ 0	$ 579.4	$ 0
Depreciation	855.9	848.9	578.4
Finite-Lived Intangible Assets, Amortization Expense	$ 256.2	235.8	131.1
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member] | Specialty Chemicals Business [Member]
Depreciation, depletion and amortization		57.2	22
Impairment of Specialty Chemicals goodwill and intangibles		579.4	0
Capital expenditures		(45.2)	(28.6)
Depreciation		30.4	11.4
Finite-Lived Intangible Assets, Amortization Expense		$ 26.8	$ 10.6

Assets Held For Sale (Details)

Assets Held For Sale (Details) - USD ($) $ in Millions	Feb. 23, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of HH&B						$ 1,005.9	$ 0	$ 0
Assets held for sale		$ 173.6				173.6	52.3
Gain on sale of HH&B		2.2	$ 190.6	$ 0	$ 0	192.8	$ 0	$ 0
Home, Health and Beauty Business [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of HH&B	$ 1,025
Foreign Pension Liabilities Divested Due to Sale of Business	$ 25
Gain on sale of HH&B						192.8
Land and Development Portfolio Assets [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale		$ 150.4				$ 150.4

Restructuring and Other Costs64

Restructuring and Other Costs, Net (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									$ 113.4	$ 294.9	$ 60.3
Restructuring and Related Cost, Cost Incurred to Date	$ 554.4								554.4
Restructuring and Related Cost, Expected Cost	567.1								567.1
Acquisition costs									27.1	8.9	44.4
Divestiture costs									9.8	0.5	0
Integration costs									41.2	59.8	36.8
Other costs									83.3	71.5	80.5
Restructuring and other costs, net, noncash									86.6	200.2	13.4
Restructuring and other costs, net	38	$ 59.4	$ 18.3	$ 81	$ 49.4	$ 43.1	$ 111.1	$ 162.8	196.7	366.4	140.8
Recategorization of Certain Restructuring and Related Costs from Integration Costs									17.4	42.6	48.2
Net Property, Plant and Equipment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									31.6	189.5	2.2
Restructuring and Related Cost, Cost Incurred to Date	261.7								261.7
Restructuring and Related Cost, Expected Cost	261.7								261.7
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									47.3	69.5	50.4
Restructuring and Related Cost, Cost Incurred to Date	190.9								190.9
Restructuring and Related Cost, Expected Cost	193.9								193.9
Equipment and Inventory Relocation Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									4.7	1.4	1.6
Restructuring and Related Cost, Cost Incurred to Date	11.4								11.4
Restructuring and Related Cost, Expected Cost	16.4								16.4
Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									6.1	19.4	3.9
Restructuring and Related Cost, Cost Incurred to Date	38.8								38.8
Restructuring and Related Cost, Expected Cost	43.5								43.5
Other Costs Related to Restructuring and Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									23.7	15.1	2.2
Restructuring and Related Cost, Cost Incurred to Date	51.6								51.6
Restructuring and Related Cost, Expected Cost	51.6								51.6
Other Segments [Member]
Restructuring Cost and Reserve [Line Items]
Acquisition costs									27.1	8.9	44.4
Divestiture costs									9.8	0.5	0
Integration costs									46.4	62.1	36.1
Other costs									83.3	71.5	80.5
Corrugated Packaging [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									10.8	230.2	8
Restructuring and Related Cost, Cost Incurred to Date	327.6								327.6
Restructuring and Related Cost, Expected Cost	335.3								335.3
Corrugated Packaging [Member] | Net Property, Plant and Equipment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									1.4	184.5	1.3
Restructuring and Related Cost, Cost Incurred to Date	221								221
Restructuring and Related Cost, Expected Cost	221								221
Corrugated Packaging [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									3.3	17.4	0.4
Restructuring and Related Cost, Cost Incurred to Date	43.2								43.2
Restructuring and Related Cost, Expected Cost	45.1								45.1
Corrugated Packaging [Member] | Equipment and Inventory Relocation Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									1.9	0.3	1.1
Restructuring and Related Cost, Cost Incurred to Date	6.5								6.5
Restructuring and Related Cost, Expected Cost	9								9
Corrugated Packaging [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									5.4	18.9	3
Restructuring and Related Cost, Cost Incurred to Date	36.4								36.4
Restructuring and Related Cost, Expected Cost	39.7								39.7
Corrugated Packaging [Member] | Other Costs Related to Restructuring and Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									(1.2)	9.1	2.2
Restructuring and Related Cost, Cost Incurred to Date	20.5								20.5
Restructuring and Related Cost, Expected Cost	20.5								20.5
Consumer Packaging [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									78.4	10	4.4
Restructuring and Related Cost, Cost Incurred to Date	99.9								99.9
Restructuring and Related Cost, Expected Cost	103.8								103.8
Consumer Packaging [Member] | Net Property, Plant and Equipment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									28.3	3.8	0.9
Restructuring and Related Cost, Cost Incurred to Date	37.5								37.5
Restructuring and Related Cost, Expected Cost	37.5								37.5
Consumer Packaging [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									26.4	4.6	1.8
Restructuring and Related Cost, Cost Incurred to Date	34.4								34.4
Restructuring and Related Cost, Expected Cost	34.4								34.4
Consumer Packaging [Member] | Equipment and Inventory Relocation Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									2.8	1.1	0.5
Restructuring and Related Cost, Cost Incurred to Date	4.9								4.9
Restructuring and Related Cost, Expected Cost	7.4								7.4
Consumer Packaging [Member] | Facility Closing [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									0.7	0.5	0.9
Restructuring and Related Cost, Cost Incurred to Date	2.4								2.4
Restructuring and Related Cost, Expected Cost	3.8								3.8
Consumer Packaging [Member] | Other Costs Related to Restructuring and Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									20.2	0	0.3
Restructuring and Related Cost, Cost Incurred to Date	20.7								20.7
Restructuring and Related Cost, Expected Cost	20.7								20.7
Land and Development [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									4.6	10.6	0
Restructuring and Related Cost, Cost Incurred to Date	15.2								15.2
Restructuring and Related Cost, Expected Cost	16.3								16.3
Land and Development [Member] | Net Property, Plant and Equipment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									1.8	0	0
Restructuring and Related Cost, Cost Incurred to Date	1.8								1.8
Restructuring and Related Cost, Expected Cost	1.8								1.8
Land and Development [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									2.8	10.6	0
Restructuring and Related Cost, Cost Incurred to Date	13.4								13.4
Restructuring and Related Cost, Expected Cost	14.5								14.5
Corporate Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									19.6	44.1	47.9
Restructuring and Related Cost, Cost Incurred to Date	111.7								111.7
Restructuring and Related Cost, Expected Cost	111.7								111.7
Corporate Segment [Member] | Net Property, Plant and Equipment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									0.1	1.2	0
Restructuring and Related Cost, Cost Incurred to Date	1.4								1.4
Restructuring and Related Cost, Expected Cost	1.4								1.4
Corporate Segment [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									14.8	36.9	48.2
Restructuring and Related Cost, Cost Incurred to Date	99.9								99.9
Restructuring and Related Cost, Expected Cost	99.9								99.9
Corporate Segment [Member] | Other Costs Related to Restructuring and Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred									4.7	$ 6	$ (0.3)
Restructuring and Related Cost, Cost Incurred to Date	10.4								10.4
Restructuring and Related Cost, Expected Cost	$ 10.4								10.4
Customer Relationships [Member] | Consumer Packaging [Member]
Restructuring Cost and Reserve [Line Items]
Impairment of Intangible Assets, Finite-lived									$ 17.6

Restructuring and Other Costs65

Restructuring and Other Costs, Net Restructuring Accrual (Details) - USD ($) $ in Millions	Jun. 06, 2017	Jul. 01, 2015	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring and other costs reserve			$ 47.4			$ 44.8	$ 44.8			$ 21.4	$ 44.8	$ 21.4	$ 10.9
Restructuring and other costs, net			38	$ 59.4	$ 18.3	81	49.4	$ 43.1	$ 111.1	162.8	196.7	366.4	140.8
Restructuring Reserve [Roll Forward]
Accrual at beginning of fiscal year						$ 44.8				$ 21.4	44.8	21.4	10.9
Accruals acquired in purchase accounting												0
Additional accruals											63.2	75.3	37.6
Payments											(53.3)	(51.9)	(31.4)
Adjustment to accruals											(10.8)	0	1.4
Accrual at end of fiscal year			$ 47.4				$ 44.8				$ 47.4	$ 44.8	$ 21.4
MPS [Member]
Restructuring Reserve [Roll Forward]
Accruals acquired in purchase accounting	$ 3.5
MeadWestvaco [Member]
Restructuring Reserve [Roll Forward]
Accruals acquired in purchase accounting		$ 2.9

Restructuring and Other Costs66

Restructuring and Other Costs, Net Restructuring Costs (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Restructuring Cost and Reserve [Line Items]
Additional accruals and adjustments to accruals (see table above)									$ 52.4	$ 75.3	$ 39
Acquisition costs									27.1	8.9	44.4
Divestiture costs									9.8	0.5	0
Integration costs									41.2	59.8	36.8
Net property, plant and equipment									31.6	189.5	2.2
Severance and other employee costs									3.8	11.5	12.7
Equipment and inventory relocation costs									4.7	1.4	1.6
Facility carrying costs									6.1	19.5	3.9
Other costs									20	0	0.2
Restructuring and other costs, net	$ 38	$ 59.4	$ 18.3	$ 81	$ 49.4	$ 43.1	$ 111.1	$ 162.8	$ 196.7	$ 366.4	$ 140.8

Other Intangible Assets (Detail

Other Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	16 years 7 months
Gross Carrying Amount	$ 4,227	$ 3,287.4
Accumulated Amortization	(897.7)	(688.1)
Finite-Lived Intangible Assets, Amortization Expense	256.2	235.8	$ 131.1
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Fiscal 2,018	294.1
Fiscal 2,019	292.1
Fiscal 2,020	281.3
Fiscal 2,021	234.6
Fiscal 2,022	$ 225.3
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	16 years 8 months
Gross Carrying Amount	$ 4,046.2	3,094.4
Accumulated Amortization	$ (806)	(610.5)
Favorable Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	9 years 7 months
Gross Carrying Amount	$ 48.2	48.9
Accumulated Amortization	$ (30.7)	(27)
Technology and Patents [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	10 years 8 months
Gross Carrying Amount	$ 31.8	55.4
Accumulated Amortization	$ (14.4)	(14.9)
Trademarks and Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	16 years 4 months
Gross Carrying Amount	$ 74.7	65
Accumulated Amortization	$ (31.4)	(24.1)
Noncompete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	2 years
Gross Carrying Amount	$ 2.5	0.2
Accumulated Amortization	$ (0.6)	(0.1)
Licensing Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	8 years 9 months
Gross Carrying Amount	$ 23.6	23.5
Accumulated Amortization	$ (14.6)	$ (11.5)

Debt (Details)

Debt (Details) € in Millions, $ in Millions

Oct. 31, 2017USD ($)

Aug. 24, 2017USD ($)

Jul. 22, 2016USD ($)

Jun. 22, 2016USD ($)

Jul. 01, 2015USD ($)

Sep. 30, 2017USD ($)

Sep. 30, 2016USD ($)

Sep. 30, 2015USD ($)

Jun. 30, 2017USD ($)

May 15, 2017USD ($)

Mar. 02, 2017EUR (€)

Mar. 24, 2016USD ($)

Mar. 04, 2016USD ($)

Feb. 11, 2016USD ($)

Dec. 01, 2015USD ($)

Debt Instrument [Line Items]

Unamortized Fair Market Value Step-Up

$ 281.8

Unamortized Fair Market Value Step-Up, Weighted Average Remaining Life

12 years 8 months

Weighted Average Interest Rate Excluding Fair Value Step-Up

4.10%

Long-term debt

$ 6,554.8

$ 5,789.2

Debt, Weighted Average Interest Rate

3.60%

3.30%

Current portion of debt

$ 608.7

$ 292.9

Long-term debt due after one year

5,946.1

5,496.3

Amortization of Debt Issuance Costs

4.5

4.6

$ 9.3

Fair value of debt

6,800

6,000

Letters of credit outstanding, amount

114.6

MeadWestvaco [Member]

Debt Instrument [Line Items]

Fair value step-up

$ 364.5

MeadWestvaco [Member] | Maximum [Member]

Debt Instrument [Line Items]

Adjustment to Fair Value Debt Assumed in Business Combination, Amortization Period

32 years

MeadWestvaco [Member] | Minimum [Member]

Debt Instrument [Line Items]

Adjustment to Fair Value Debt Assumed in Business Combination, Amortization Period

1 year

Notes Due Fiscal 2017 to 2022 [Member] | Unsecured Debt [Member]

Debt Instrument [Line Items]

Long-term debt

$ 1,484.5

$ 1,651

Debt, Weighted Average Interest Rate

4.20%

3.90%

Revolver, Receivables Facility and Term Loan [Member]

Debt Instrument [Line Items]

Line of credit facility, remaining borrowing capacity

$ 2,900

Uncommitted Credit Facilities [Member]

Debt Instrument [Line Items]

Debt Instrument, Maximum Borrowing Capacity, Amount

100

Notes Due Fiscal 2017 to 2022 [Member] | Unsecured Debt [Member]

Debt Instrument [Line Items]

Long-term debt

$ 500

Interest rate

3.00%

Debt Instrument, Unamortized Discount

$ 1.4

Debt Instrument, Interest Rate, Effective Percentage

3.18%

Deferred Finance Costs, Current, Gross

$ 4.2

Senior Notes due September 15, 2027 [Member] | Unsecured Debt [Member]

Debt Instrument [Line Items]

Long-term debt

$ 500

Interest rate

3.375%

Debt Instrument, Unamortized Discount

$ 0.2

Debt Instrument, Interest Rate, Effective Percentage

3.48%

Deferred Finance Costs, Current, Gross

$ 4.3

Long-term Debt, Excluding Capital Lease Obligations [Member]

Debt Instrument [Line Items]

Long-term debt

6,377.8

Fiscal 2,018

603.6

Fiscal 2,019

724.5

Fiscal 2,020

1,499.8

Fiscal 2,021

0

Fiscal 2,022

1,000

Thereafter

2,309.2

Fair Value of Debt Step-Up, Deferred Financing Costs and Unamortized Bond Discounts

240.7

Capital Lease Obligations [Member] | Secured Debt [Member]

Debt Instrument [Line Items]

Long-term debt

$ 177

$ 184.4

Debt, Weighted Average Interest Rate

4.30%

4.20%

Fiscal 2,018

$ 5.6

Fiscal 2,019

4.5

Fiscal 2,020

3.4

Fiscal 2,021

2.1

Fiscal 2,022

2.1

Thereafter

138.7

Fair value step-up

20.6

Supplier Financing and Commercial Card Programs [Member] | Unsecured Debt [Member]

Debt Instrument [Line Items]

Long-term debt

130.3

$ 106

Notes Due Fiscal 2023 to 2027 [Member] | Unsecured Debt [Member]

Debt Instrument [Line Items]

Long-term debt

$ 1,368.8

$ 411.8

Debt, Weighted Average Interest Rate

3.60%

4.30%

Notes Due Fiscal 2030 to 2033 [Member] | Unsecured Debt [Member]

Debt Instrument [Line Items]

Long-term debt

$ 975.5

$ 987.5

Debt, Weighted Average Interest Rate

5.20%

4.70%

Notes Due Fiscal 2037 to 2047 [Member] | Unsecured Debt [Member]

Debt Instrument [Line Items]

Long-term debt

$ 178.8

$ 179.2

Debt, Weighted Average Interest Rate

6.30%

6.00%

Credit Facility [Member] | Unsecured Debt [Member] | Maximum [Member]

Debt Instrument [Line Items]

Facility commitment

0.25%

Credit Facility [Member] | Unsecured Debt [Member] | Minimum [Member]

Debt Instrument [Line Items]

Facility commitment

0.125%

Credit Facility [Member] | Unsecured Debt [Member] | LIBOR Based Borrowings [Member]

Debt Instrument [Line Items]

Applicable margin

1.125%

Credit Facility [Member] | Unsecured Debt [Member] | LIBOR Based Borrowings [Member] | Maximum [Member]

Debt Instrument [Line Items]

Applicable margin

1.50%

Credit Facility [Member] | Unsecured Debt [Member] | LIBOR Based Borrowings [Member] | Minimum [Member]

Debt Instrument [Line Items]

Applicable margin

1.00%

Credit Facility [Member] | Unsecured Debt [Member] | Base Rate [Member]

Debt Instrument [Line Items]

Applicable margin

0.125%

Credit Facility [Member] | Unsecured Debt [Member] | Base Rate [Member] | Maximum [Member]

Debt Instrument [Line Items]

Applicable margin

0.50%

Credit Facility [Member] | Unsecured Debt [Member] | Base Rate [Member] | Minimum [Member]

Debt Instrument [Line Items]

Applicable margin

0.00%

Revolving Credit Facility [Member] | Future Mexican Peso Sub-Facility [Member]

Debt Instrument [Line Items]

Credit Facility, maximum borrowing capacity

$ 200

Revolving Credit Facility [Member] | Letter of Credit [Member]

Debt Instrument [Line Items]

Capacity available for special purpose

150

Revolving Credit Facility [Member] | Canadian Dollar Borrowing [Member]

Debt Instrument [Line Items]

Capacity available for special purpose

400

Revolving Credit Facility [Member] | Unsecured Debt [Member]

Debt Instrument [Line Items]

Long-term debt

$ 0

$ 0

Credit Facility, maximum borrowing capacity

$ 2,000

Debt Instrument, Term, in Years

5 years

Committed Principal Amount Extended to July 1, 2022

$ 1,900

Term Loan Facility [Member] | Unsecured Debt [Member]

Debt Instrument [Line Items]

Long-term debt

1,023.5

1,596.7

Credit Facility, maximum borrowing capacity

$ 2,300

Amount Drawn on Unsecured Term Loan

1,200

Amount Which Can Be Drawn On A Delayed Draw Basis Not Later Than Nine Months After the Closing of the Credit Agreement

$ 1,100

Prepayment of Amortization Payments

575

$ 200

Amount Drawn On Delayed Draw Term Loan

$ 600

Debt Instrument, Term, in Years

5 years

Term Loan Facilities [Member] | Unsecured Debt [Member]

Debt Instrument [Line Items]

Long-term debt

$ 1,622.7

$ 2,195.7

Debt, Weighted Average Interest Rate

2.50%

1.80%

Farm Credit Facility [Member] | Unsecured Debt [Member]

Debt Instrument [Line Items]

Long-term debt

$ 599.2

$ 599

Credit Facility, maximum borrowing capacity

$ 600

Debt Instrument, Term, in Years

7 years

Revolving Credit and Swing Facilities [Member] | Unsecured Debt [Member]

Debt Instrument [Line Items]

Long-term debt

$ 436.4

0

Debt, Weighted Average Interest Rate

1.10%

Receivables Facility [Member] | Secured Debt [Member]

Debt Instrument [Line Items]

Long-term debt

$ 110

$ 0

Debt, Weighted Average Interest Rate

2.10%

Debt Instrument, Interest Rate, Effective Percentage

2.20%

1.40%

Prepayment of Debt

$ 415

Applicable margin

0.85%

Receivables backed financing, maximum borrowing amount

$ 700

Restriction on Exclusion of Eligible Receivables of Specific Obligors, Aggregate Maximum Percentage

7.50%

Restriction on Exclusion of Eligible Receivables of Specific Obligors, Obligor Maximum Percentage of Aggregate Balance

2.50%

Asset Securitization Facility Commitment Fee Percentage

0.25%

0.25%

Debt Instrument, Maximum Borrowing Capacity, Amount

$ 577.6

$ 584.3

Loans and Leases Receivable, Collateral for Secured Borrowings

848.3

International and Other Debt [Member]

Debt Instrument [Line Items]

Long-term debt

$ 70.8

$ 73.6

Debt, Weighted Average Interest Rate

6.80%

7.30%

Public Bond Obligations

Debt Instrument [Line Items]

Debt Instrument, Face Amount

$ 3,800

$ 2,900

Subsequent Event [Member] | Term Loan Facility [Member] | Unsecured Debt [Member]

Debt Instrument [Line Items]

Prepayment of Amortization Payments

$ 485

Unsecured Debt [Member] | Sumitomo Revolving Line of Credit [Member]

Debt Instrument [Line Items]

Current portion of debt

106.7

0

Credit Facility, maximum borrowing capacity

$ 200

Unsecured Debt [Member] | Bank of Tokyo-Mitsubishi UFJ, LTD Line of Credit [Member]

Debt Instrument [Line Items]

Current portion of debt

0

Credit Facility, maximum borrowing capacity

$ 100

Unsecured Debt [Member] | Cooperatieve Rabobank U.A., New York Branch Revolving Line of Credit [Member]

Debt Instrument [Line Items]

Current portion of debt

118.1

$ 0

Credit Facility, maximum borrowing capacity

€ 100

$ 100

Unsecured Debt [Member] | Cooperatieve Rabobank U.A., New York Branch European Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Current portion of debt

$ 211.6

Credit Facility, maximum borrowing capacity

$ 600

Line of Credit Facility, Maximum Euro Denominated Borrowing Capacity

200

Line of Credit Facility, Maximum Sterling Denominated Borrowing Capacity

$ 400

Fair Value (Details)

Fair Value (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 29, 2017	Jun. 27, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Loss on Sale of Accounts Receivable for Fiscal Year					$ 8
Land and Development impairment	$ 4	$ 0	$ 42.7	$ 0	46.7	$ 0	$ 0
Maximum Eligible Receivables That May Be Sold								$ 490	$ 400
Receivable from financial institution at beginning of fiscal year				$ 13.8	13.8	5.8
Receivables sold to the financial institution and derecognized	1,542.5				1,542.5	1,474.6
Receivables collected by financial institution					(1,466.7)	(1,367.2)
Cash proceeds from financial institution					(64.7)	(99.4)
Receivable from financial institution at September 30,	$ 24.9				24.9	$ 13.8	$ 5.8
Consumer Packaging [Member] | Customer Relationships [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of Intangible Assets, Finite-lived					$ 17.6

Leases (Details)

Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Operating Leased Assets [Line Items]
Fiscal 2,018	$ 123.3
Fiscal 2,019	103.5
Fiscal 2,020	86.3
Fiscal 2,021	68.8
Fiscal 2,022	54.5
Thereafter	188.6
Total future minimum lease payments	625
Rental expense	$ 210.5	$ 199.3	$ 144.8

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Deferred Tax Assets, Gross	$ 884.5	$ 827.4
Income (loss) from continuing operations:
United States	481.9	(25.1)	$ 571.3
Foreign	375.7	269.7	162.9
Income from continuing operations before income taxes	857.6	244.6	734.2
Deferred income taxes:
Total deferred (benefit) expense	(20.4)	(160.9)	161.4
Total income tax expense	159	89.8	233
Operating Loss Carryforwards	61.2	85.3
Federal and foreign net operating loss carryforwards	$ 204.1	119.3
Minimum [Member]
Operating loss carryforward expiration	Oct. 1, 2030
Maximum [Member]
Operating loss carryforward expiration	Sep. 30, 2037
Foreign Country [Member]
Deferred income taxes:
Operating Loss Carryforwards	$ 673.7	448.7
Operating Loss Carryforwards, Valuation Allowance	149.6	92.5
Federal and foreign net operating loss carryforwards	$ 182.6	119.3
Foreign Country [Member] | Minimum [Member]
Operating loss carryforward expiration	Oct. 1, 2018
Foreign Country [Member] | Maximum [Member]
Operating loss carryforward expiration	Sep. 30, 2037
Continuing Operations [Member]
Current income taxes:
Federal	$ 80.8	98.3	31.6
State	3.3	12.8	7.3
Foreign	95.3	87	38.6
Total current expense	179.4	198.1	77.5
Deferred income taxes:
Federal	15.2	(131.5)	157.8
State	(22.8)	6.9	(10.8)
Foreign	(12.8)	16.3	8.5
Total deferred (benefit) expense	(20.4)	(108.3)	155.5
Total income tax expense	$ 159	$ 89.8	$ 233

Income Taxes Effective Tax Rate

Income Taxes Effective Tax Rate Reconciliation (Details) - Continuing Operations [Member]	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Statutory federal tax rate	35.00%	35.00%	35.00%
Foreign rate differential	(4.90%)	(5.50%)	(1.60%)
Adjustment and resolution of federal, state and foreign tax uncertainties	(0.30%)	0.20%	0.30%
State taxes, net of federal benefit	3.30%	4.90%	1.20%
Research and development and other tax credits, net of valuation allowances and reserves	(0.80%)	(6.10%)	(0.10%)
Income attributable to noncontrolling interest	0.40%	0.80%	(0.40%)
Domestic manufacturer’s deduction	(2.00%)	(4.40%)	(2.60%)
Sale of HH&B	(5.00%)	0.00%	0.00%
U.S. legal entity restructuring	(3.30%)	0.00%	0.00%
Change in valuation allowance	(3.30%)	6.30%	(0.80%)
Nondeductible transaction costs	1.00%	0.40%	1.00%
Contribution of assets to Grupo Gondi joint venture	0.00%	3.40%	0.00%
Nontaxable increased cash surrender value	(1.50%)	(4.60%)	(0.10%)
Withholding taxes	0.40%	2.00%	0.00%
Brazilian net worth deduction	(0.80%)	(2.00%)	(0.10%)
Other, net	0.30%	6.30%	(0.10%)
Effective tax rate	18.50%	36.70%	31.70%

Income Taxes Deferred Taxes (De

Income Taxes Deferred Taxes (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016
Deferred income tax assets:
Accruals and allowances		$ 40.6	$ 12.2
Employee related accruals and allowances		265.1	217.6
Pension obligations		0	15.5
State net operating loss carryforwards		70.6	82.3
State credit carryforwards, net of federal benefit		54.4	56.1
U.S. and foreign tax credit carryforwards		135.9	185.1
Federal and foreign net operating loss carryforwards		204.1	119.3
Restricted stock and options		81	94.9
Other		32.8	44.4
Deferred Tax Assets, Gross		884.5	827.4
Deferred income tax liabilities:
Property, plant and equipment		2,154.1	2,124
Deductible intangibles and goodwill		1,091.4	891.3
Inventory reserves		236.1	205.6
Deferred gain		405.2	432.1
Pension obligations		90.8	0
Basis difference in joint ventures		57.1	96
Other		8.3	1
Deferred Tax Liabilities, Gross		4,043	3,750
Valuation allowances		219.1	177.2
Net deferred income tax liability		3,377.6	3,099.8
Long-term deferred tax asset	[1]	32.6	30.9
Long-term deferred tax liability		3,410.2	3,130.7
Operating Loss Carryforwards		61.2	85.3
Undistributed Foreign Earnings		2,300
State and Local Jurisdiction [Member]
Deferred income tax assets:
State net operating loss carryforwards		70.6	82.3
Deferred income tax liabilities:
Operating Loss Carryforwards		1,885	1,899
Operating Loss Carryforwards, Valuation Allowance		15.9	14.2
Tax Credit Carryforward, Deferred Tax Asset		54.4	56.1
Tax credit carryforward, valuation allowance		47.3	51.2
Foreign Country [Member]
Deferred income tax assets:
Federal and foreign net operating loss carryforwards		182.6	119.3
Deferred income tax liabilities:
Operating Loss Carryforwards		673.7	448.7
Operating Loss Carryforwards, Valuation Allowance		$ 149.6	92.5
Minimum [Member]
Deferred income tax liabilities:
Operating loss carryforward expiration		Oct. 1, 2030
Minimum [Member] | State and Local Jurisdiction [Member]
Deferred income tax liabilities:
Operating loss carryforward expiration		Oct. 1, 2018
Tax Credit Carryforward, Years to Expiration		5 years
Minimum [Member] | Foreign Country [Member]
Deferred income tax liabilities:
Operating loss carryforward expiration		Oct. 1, 2018
Maximum [Member]
Deferred income tax liabilities:
Operating loss carryforward expiration		Sep. 30, 2037
Maximum [Member] | State and Local Jurisdiction [Member]
Deferred income tax liabilities:
Operating loss carryforward expiration		Sep. 30, 2037
Tax Credit Carryforward, Years to Expiration		10 years
Maximum [Member] | Foreign Country [Member]
Deferred income tax liabilities:
Operating loss carryforward expiration		Sep. 30, 2037
Alternative Minimum Tax Credits [Member]
Deferred income tax liabilities:
Tax credit carryforward		$ 132.2	$ 185.1
Research Tax Credit Carryforward [Member]
Deferred income tax liabilities:
Tax credit carryforward		3.2
General Business Tax Credit Carryforward [Member]
Deferred income tax liabilities:
Tax credit carryforward		$ 0.5
[1]	The long-term deferred tax asset is presented in Other assets on the Consolidated Balance Sheets.

Income Taxes Valuation Allowanc

Income Taxes Valuation Allowance Against Deferred Tax Assets (Details) - Valuation Allowance of Deferred Tax Assets [Member] - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2015
Movement in Deferred Tax Asset Valuation Allowance [Roll Forward]
Balance at beginning of fiscal year	$ 177.2		$ 100.2		$ 65.1
Increases	54.3		24.8		2.7
Allowances related to purchase accounting	12.4	[1]	63	[1]	40
Reductions	(24.8)		(10.8)		(7.6)
Balance at end of fiscal year	$ 219.1		$ 177.2		$ 100.2
[1]	Adjustments in fiscal 2017 relate to the MPS Acquisition. Adjustments in fiscal 2016 relate to the Combination and the SP Fiber Acquisition. Adjustments in fiscal 2015 relate to the Combination

Income Taxes Unrecognized Tax B

Income Taxes Unrecognized Tax Benefit (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		$ 138	$ 138.6
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of fiscal year		166.8	106.6	$ 36.5
Additions related to purchase accounting	[1]	7.7	16.5	82.9
Additions for tax positions taken in current year		5	30.3	2.4
Additions for tax positions taken in prior fiscal years		15.2	20.6	0
Reductions for tax positions taken in prior fiscal years		(25.6)	(9.7)	(3.7)
Reductions due to settlement	[2]	(14.1)	(1.3)	0
Additions for currency translation adjustments		2	7
Reductions for currency translation adjustments				(11.5)
Reductions as a result of a lapse of the applicable statute of limitations		(8.1)	(3.2)	0
Balance at end of fiscal year		148.9	166.8	106.6
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued		81.7	60.2
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense		5.4	$ 7.4	$ 2.9
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 29.6
[1]	Adjustments in fiscal 2017 relate to the MPS Acquisition. Adjustments in fiscal 2016 relate to the Combination and the SP Fiber Acquisition. Adjustments in fiscal 2015 relate to the Combination
[2]	Reductions due to settlement in fiscal 2017 relate to the settlement of federal and state audit examinations with taxing authorities.

Retirement Plans (Details)

Retirement Plans (Details) - USD ($) $ in Millions	Jul. 30, 2015	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Adjustment to RP-2014 Table White Collar Males									9.00%	6.00%
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)						$ 32.5
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax							$ (3.9)
Pension lump sum settlement and retiree medical curtailment, net		$ 3.9	$ 0	$ 28.7	$ 0	20			$ 32.6	$ 0	$ 11.5
Adjustment to RP-2014 Table Males											6.00%
Minimum Age to Continue to Accrue Pension Plan Benefits	50 years
Gain Recorded to Other Comprehensive Income Related to the Settlement and Remeasurement of Pension Offer						28.6
Defined Benefit Plan, Accumulated Benefit Obligation, Increase (Decrease) for Plan Amendment							$ 22.1
Aggregate Age and Service to Continue to Accrue Pension Plan Benefits	75 years
Adjustment to RP-2014 tables white collar females									11.00%	12.00%	13.00%
Adjustment to RP-2014 tables blue collar female									9.00%	19.00%	19.00%
Adjustment to RP-2014 Table Blue Collar Males									12.00%	10.00%
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement						163.7
Defined Benefit Plan, Plan Assets, Payment for Settlement						$ 135.1		$ 27.1
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year		39						39	$ 39
Other Pension, Postretirement and Supplemental Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension and other postretirement plans, assets		168.9						168.9	168.9
Pension and other postretirement plans, liabilities		176.2						176.2	176.2
Foreign Plan [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)									(57.6)	$ 70.8
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax		$ (173.9)						$ (173.9)	$ (173.9)	$ (195.8)
Defined Benefit Plan, Target Allocation Percentage of Assets		100.00%						100.00%	100.00%	100.00%
Defined Benefit Plan, Actual Plan Asset Allocations		100.00%						100.00%	100.00%	100.00%
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement									$ (0.4)	$ (0.1)
Defined Benefit Plan, Plan Assets, Payment for Settlement									$ 0.4	$ 0.1
Foreign Plan [Member] | Equity Securities [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Target Allocation Percentage of Assets		24.00%						24.00%	24.00%	28.00%
Defined Benefit Plan, Actual Plan Asset Allocations		26.00%						26.00%	26.00%	29.00%
Foreign Plan [Member] | Fixed Income Funds [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Target Allocation Percentage of Assets		65.00%						65.00%	65.00%	59.00%
Defined Benefit Plan, Actual Plan Asset Allocations		64.00%						64.00%	64.00%	59.00%
Foreign Plan [Member] | Short-term Investments [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Target Allocation Percentage of Assets		1.00%						1.00%	1.00%	1.00%
Defined Benefit Plan, Actual Plan Asset Allocations		3.00%						3.00%	3.00%	2.00%
Foreign Plan [Member] | Other Investments [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Target Allocation Percentage of Assets		10.00%						10.00%	10.00%	12.00%
Defined Benefit Plan, Actual Plan Asset Allocations		7.00%						7.00%	7.00%	10.00%
Domestic Plan [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)									$ (149.1)	$ 664.2
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax		$ (547.3)						$ (547.3)	(547.3)	$ (633.4)
Defined Benefit Plan, Plan with Benefit Obligation in Excess of Plan Assets, Benefit Obligation		$ 204.6						$ 204.6	$ 204.6
Defined Benefit Plan, Target Allocation Percentage of Assets		100.00%						100.00%	100.00%	100.00%
Defined Benefit Plan, Actual Plan Asset Allocations		100.00%						100.00%	100.00%	100.00%
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation		$ 201.9						$ 201.9	$ 201.9
Defined Benefit Plan, Plan with Benefit Obligation in Excess of Plan Assets, Fair Value of Plan Assets		$ 30.2						$ 30.2	30.2
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement									(229.3)	$ (2,484.6)
Defined Benefit Plan, Plan Assets, Payment for Settlement									$ 229.3	$ 2,484.6
Domestic Plan [Member] | Equity Securities [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Target Allocation Percentage of Assets		15.00%						15.00%	15.00%	14.00%
Defined Benefit Plan, Actual Plan Asset Allocations		13.00%						13.00%	13.00%	15.00%
Domestic Plan [Member] | Fixed Income Funds [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Target Allocation Percentage of Assets		70.00%						70.00%	70.00%	71.00%
Defined Benefit Plan, Actual Plan Asset Allocations		73.00%						73.00%	73.00%	66.00%
Domestic Plan [Member] | Short-term Investments [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Target Allocation Percentage of Assets		1.00%						1.00%	1.00%	1.00%
Defined Benefit Plan, Actual Plan Asset Allocations		3.00%						3.00%	3.00%	7.00%
Domestic Plan [Member] | Other Investments [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Target Allocation Percentage of Assets		14.00%						14.00%	14.00%	14.00%
Defined Benefit Plan, Actual Plan Asset Allocations		11.00%						11.00%	11.00%	12.00%

Retirement Plans Assumptions (D

Retirement Plans Assumptions (Details) - USD ($) $ in Millions	Sep. 21, 2016	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Sep. 30, 2017	Jun. 30, 2015	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Feb. 28, 2017
Defined Benefit Plan Disclosure [Line Items]
Percentage Reduction of Overall U.S. Pension Obligations and Assets in Connection with Settlement	40.00%
Adjustment to RP-2014 Table White Collar Males														9.00%	6.00%
Adjustment to RP-2014 Table Males																6.00%
Adjustment to RP-2014 Table Blue Collar Males														12.00%	10.00%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate						4.04%									4.04%		4.49%
Defined Benefit Plan, Increase in Funded Status																	$ 73.2
Settlements									$ 135.1		$ 27.1
Adjustment to RP-2014 tables white collar females														11.00%	12.00%	13.00%
Adjustment to RP-2014 tables blue collar female														9.00%	19.00%	19.00%
Plan Assets Used to Settle Pension Obligations Plan by Purchasing Group Annuity Contracts from Prudential	$ 2,500
Retirement Benefits Payment Responsibility Moved to Prudential Owed to U.S. Retirees and Their Beneficiaries, Number	35,000
Pension risk transfer expense	$ 370.7					$ 370.7	$ 0	$ 0	0					$ 0	$ 370.7	$ 0
Pension lump sum settlement and retiree medical curtailment, net		$ 3.9	$ 0	$ 28.7	$ 0				$ 20					32.6	$ 0	$ 11.5
Lump Sum Payment Related to Pension Settlement Made Out of Existing Plan Assets				$ 203.7										$ 230.8
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated Amount of Aggregate Pension Benefit Obligation Related to Partial Settlement												$ 0.6
Pension lump sum settlement and retiree medical curtailment, net										$ 8.1		$ 8.5
Domestic Plan [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		4.09%				4.04%					4.09%			4.09%	4.04%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate														4.04%	4.70%	4.52%
Domestic Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		4.09%				4.04%					4.09%			4.09%	4.04%
Settlements														$ 229.3	$ 2,484.6
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase		3.00%				3.00%					3.00%			3.00%	3.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets														6.50%	5.88%	7.11%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate														4.30%	4.70%	4.52%
Defined Benefit Plan, Assumptions Used Caclulating Net Periodic Cost, Rate of Compensation Increase		3.00%				2.50%					3.00%			3.00%	2.50%	2.54%
Domestic Plan [Member] | Scenario, Forecast [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets													6.50%
Foreign Plan [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		6.51%				6.64%					6.51%			6.51%	6.64%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase														7.37%	3.14%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate														6.64%	6.84%	4.00%
Defined Benefit Plan, Assumptions Used Caclulating Net Periodic Cost, Rate of Compensation Increase		3.14%				3.10%					3.14%			3.14%	3.10%	3.00%
Foreign Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		3.26%				3.08%					3.26%			3.26%	3.08%
Settlements														$ 0.4	$ 0.1
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase		3.17%				3.09%					3.17%			3.17%	3.09%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets														6.03%	6.34%	6.88%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate														3.08%	3.89%	4.00%
Defined Benefit Plan, Assumptions Used Caclulating Net Periodic Cost, Rate of Compensation Increase		3.09%				3.10%					3.09%			3.09%	3.10%	3.00%
Foreign Plan [Member] | Scenario, Forecast [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets													4.98%

Retirement Plans Defined Benefi

Retirement Plans Defined Benefit Plan Obligations (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used, Minimum Outstanding Par Value of Bonds Used to Determine Future Discount Rate		$ 100	$ 100
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Actuarial loss (gain)	$ 32.5
Settlements	163.7
Settlements	(135.1)	(27.1)
Prepaid pension asset, non-current		368	368	$ 257.8
Defined Benefit Plan, Accumulated Benefit Obligation		5,390.7	5,390.7	5,112
Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost			45.1	51.4	$ 44.7
Interest cost			197.8	310.3	218.1
Special termination benefits			12.5	18.4	9.1
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost			0.9	2.3	1
Interest cost			7.4	8.1	5.4
Foreign Plan [Member] | Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of fiscal year	865.1		925.2	865.1
Service cost			7.1	5.7
Interest cost			32.6	32.5
Amendments			0	0
Actuarial loss (gain)			(57.6)	70.8
Plan participant contributions			1.7	1.5
Special termination benefits			0	0
Benefits paid			(65.1)	(57.5)
Business combinations			621	(0.6)
Curtailments			0	(0.5)
Settlements			(0.4)	(0.1)
Foreign currency rate changes			65.1	8.3
Other adjustments			0	0
Business divestitures			(27.4)	0
Benefit obligation at end of fiscal year		1,502.2	1,502.2	925.2	865.1
Fair value of plan assets at beginning of fiscal year	711.8		774.1	711.8
Actual gain on plan assets			2.4	82.9
Employer contributions			19.2	31.4
Plan participant contributions			1.7	1.5
Benefits paid			(65.1)	(57.5)
Business combinations			622.1	0
Settlements			(0.4)	(0.1)
Business divestitures			(0.7)	0
Foreign currency rate changes			61.4	4.1
Other adjustments			0	0
Fair value of plan assets at end of fiscal year		1,414.7	1,414.7	774.1	711.8
Over (under) funded status		(87.5)	(87.5)	(151.1)
Prepaid pension asset, non-current		27.6	27.6	10.5
Other current liability		(0.8)	(0.8)	(1.1)
Accrued pension / postretirement and other long-term benefits		(114.3)	(114.3)	(160.5)
Foreign Plan [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of fiscal year	51.6		62.6	51.6
Service cost			0.8	0.6
Interest cost			4.1	3.6
Amendments			(1)	0
Actuarial loss (gain)			0.4	5
Benefits paid			(2.7)	(2.5)
Business combinations			2	0
Curtailments			(0.3)	0
Foreign currency rate changes			2.6	4.3
Business divestitures			(0.4)	0
Benefit obligation at end of fiscal year		68.1	68.1	62.6	51.6
Fair value of plan assets at beginning of fiscal year	0		0	0
Employer contributions			2.7	2.5
Plan participant contributions			0	0
Benefits paid			(2.7)	(2.5)
Fair value of plan assets at end of fiscal year		0	0	0	0
Over (under) funded status		(68.1)	(68.1)	(62.6)
Other current liability		(3)	(3)	(2.9)
Accrued pension / postretirement and other long-term benefits		(65.1)	(65.1)	(59.7)
Domestic Plan [Member] | Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of fiscal year	6,122.3		4,231.7	6,122.3
Service cost			38	45.7
Interest cost			165.2	277.8
Amendments			3.5	1.4
Actuarial loss (gain)			(149.1)	664.2
Plan participant contributions			0	0
Special termination benefits			12.5	18.4
Benefits paid			(141.4)	(399.2)
Business combinations			0	9.9
Curtailments			0	(2.7)
Settlements			(229.3)	(2,484.6)
Foreign currency rate changes			0	0
Other adjustments			10.8	0
Business divestitures			0	(21.5)
Benefit obligation at end of fiscal year		3,941.9	3,941.9	4,231.7	6,122.3
Fair value of plan assets at beginning of fiscal year	6,481.6		4,301.5	6,481.6
Actual gain on plan assets			104.2	707.3
Employer contributions			15.3	16.1
Plan participant contributions			0	0
Benefits paid			(141.4)	(399.2)
Business combinations			0	0
Settlements			(229.3)	(2,484.6)
Business divestitures			0	(19.7)
Foreign currency rate changes			0	0
Other adjustments			57.6	0
Fair value of plan assets at end of fiscal year		4,107.9	4,107.9	4,301.5	6,481.6
Over (under) funded status		166	166	69.8
Prepaid pension asset, non-current		340.4	340.4	247.3
Other current liability		(9.3)	(9.3)	(9.9)
Accrued pension / postretirement and other long-term benefits		(165.1)	(165.1)	(167.6)
Domestic Plan [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of fiscal year	109.5		90.7	109.5
Service cost			0.1	1.7
Interest cost			3.3	4.5
Amendments			(3.4)	(4)
Actuarial loss (gain)			14.1	(6.3)
Benefits paid			(8)	(14.1)
Business combinations			1.3	0
Curtailments			0	0
Foreign currency rate changes			0	0
Business divestitures			0	(0.6)
Benefit obligation at end of fiscal year		98.1	98.1	90.7	109.5
Fair value of plan assets at beginning of fiscal year	$ 0		0	0
Employer contributions			8	14.1
Plan participant contributions			0	0
Benefits paid			(8)	(14.1)
Fair value of plan assets at end of fiscal year		0	0	0	$ 0
Over (under) funded status		(98.1)	(98.1)	(90.7)
Other current liability		(9.8)	(9.8)	(10.4)
Accrued pension / postretirement and other long-term benefits		$ (88.3)	$ (88.3)	$ (80.3)

Retirement Plans Underfunded St

Retirement Plans Underfunded Status of Pension and Postretirement Plans (Details) $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation	$ 10
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components	1
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation	$ 8

Retirement Plans Amounts in Acc

Retirement Plans Amounts in Accumulated Other Comprehensive Income (Loss) and Other Comprehensive (Income) Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss				$ 3.9
Net actuarial (gain) loss arising during period	$ (34.1)	$ 354	$ 81.5
Amortization and settlement recognition of net actuarial (loss) gain	(56.4)	(379.7)	(48.1)
Prior service cost (credit) arising during period	(1)	(2.3)	25
Amortization of prior service (cost) credit	0.4	(1.8)	7.5
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss arising during period	(48.8)	355.4	85.9
Amortization and settlement recognition of net actuarial (loss) gain	(57.7)	(381.6)	(49.2)
Prior service cost (credit) arising during period	3.4	1.5	26.4
Amortization of prior service (cost) credit	(4.1)	(3.9)	(3)
Net amount recognized in other comprehensive (income) loss	(107.2)	(28.6)	60.1
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss arising during period	14.7	(1.4)	(4.4)
Amortization and settlement recognition of net actuarial (loss) gain	1.3	1.9	1.1
Prior service cost (credit) arising during period	(4.4)	(3.8)	(1.4)
Amortization of prior service (cost) credit	4.5	2.1	10.5
Net amount recognized in other comprehensive (income) loss	16.1	(1.2)	$ 5.8
Foreign Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	173.9	195.8
Prior service cost (credit)	0.4	0.4
Total accumulated other comprehensive loss (income)	174.3	196.2
Foreign Plan [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	4.2	4.1
Prior service cost (credit)	(1.4)	(0.4)
Total accumulated other comprehensive loss (income)	2.8	3.7
Domestic Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	547.3	633.4
Prior service cost (credit)	27.6	28.2
Total accumulated other comprehensive loss (income)	574.9	661.6
Domestic Plan [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	(9.1)	(24.9)
Prior service cost (credit)	(13.9)	(14.9)
Total accumulated other comprehensive loss (income)	$ (23)	$ (39.8)

Retirement Plans Amounts Recogn

Retirement Plans Amounts Recognized in Consolidated Statement of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 45.1	$ 51.4	$ 44.7
Interest cost	197.8	310.3	218.1
Expected return on plan assets	(313.1)	(412.3)	(292.9)
Amortization of net actuarial loss (gain)	25.4	11	29
Amortization of prior service cost (credit)	4.1	3.9	3
Curtailment Gain	0	(1.6)	0
Settlement Loss	32.7	370.7	20.2
Special termination benefits	(12.5)	(18.4)	(9.1)
Company defined benefit plan expense	4.5	351.8	31.2
Multiemployer and other plans	4.7	5.8	5.6
Net pension cost (credit)	9.2	357.6	36.8
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.9	2.3	1
Interest cost	7.4	8.1	5.4
Amortization of net actuarial loss (gain)	(1.3)	(2)	(1.1)
Amortization of prior service cost (credit)	(4.5)	(2.1)	(2)
Curtailment Gain	(0.3)	0	(8.5)
Net pension cost (credit)	$ 2.2	$ 6.3	$ (5.2)

Retirement Plans Assumed Health

Retirement Plans Assumed Health Care Cost Trend Rates (Details) - Other Postretirement Benefits Plan [Member]	12 Months Ended
	Sep. 30, 2017
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rates assumed for next year	7.27%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	6.16%
Year the rate reaches the ultimate trend rate	2,029
Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rates assumed for next year	6.29%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	4.43%
Year the rate reaches the ultimate trend rate	2,037

Retirement Plans Weighted-avera

Retirement Plans Weighted-average Assumptions (Details) - Pension Plan [Member]	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on plan assets	6.50%	5.88%	7.11%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.30%	4.70%	4.52%
Defined Benefit Plan, Assumptions Used Caclulating Net Periodic Cost, Rate of Compensation Increase	3.00%	2.50%	2.54%
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on plan assets	6.03%	6.34%	6.88%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	3.08%	3.89%	4.00%
Defined Benefit Plan, Assumptions Used Caclulating Net Periodic Cost, Rate of Compensation Increase	3.09%	3.10%	3.00%

Retirement Plans Losses Amortiz

Retirement Plans Losses Amortized from Accumulated Other Comprehensive Loss into Net Periodic Benefit Cost (Details) $ in Millions	Sep. 30, 2017USD ($)
Domestic Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected Amortization of Loss (Gain), Next Fiscal Year	$ 12.2
Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year	4.3
Expected Amortization, Next Fiscal Year	16.5
Domestic Plan [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected Amortization of Loss (Gain), Next Fiscal Year	(0.9)
Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year	(4)
Expected Amortization, Next Fiscal Year	(4.9)
Foreign Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected Amortization of Loss (Gain), Next Fiscal Year	6.2
Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year	0.1
Expected Amortization, Next Fiscal Year	6.3
Foreign Plan [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected Amortization of Loss (Gain), Next Fiscal Year	0.7
Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year	(0.2)
Expected Amortization, Next Fiscal Year	$ 0.5

Retirement Plans Projected Esti

Retirement Plans Projected Estimated Benefit Payments (Details) $ in Millions	Sep. 30, 2017USD ($)
Domestic Plan [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fiscal 2,018	$ 9.8
Fiscal 2,019	8.6
Fiscal 2,020	8
Fiscal 2,021	7.6
Fiscal 2,022	7.3
Fiscal Years 2023 – 2027	32.1
Domestic Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fiscal 2,018	200.5
Fiscal 2,019	206.8
Fiscal 2,020	217.9
Fiscal 2,021	222.6
Fiscal 2,022	213.1
Fiscal Years 2023 – 2027	1,146.5
Foreign Plan [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fiscal 2,018	3
Fiscal 2,019	3.1
Fiscal 2,020	3.2
Fiscal 2,021	3.3
Fiscal 2,022	3.3
Fiscal Years 2023 – 2027	18.3
Foreign Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fiscal 2,018	82.2
Fiscal 2,019	82.6
Fiscal 2,020	81.7
Fiscal 2,021	81.9
Fiscal 2,022	81.9
Fiscal Years 2023 – 2027	$ 408.4

Retirement Plans Pension Plan A

Retirement Plans Pension Plan Assets Measured at Fair Value (Details) - USD ($) $ in Millions		Sep. 30, 2017		Sep. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at NAV		$ 2,378.7		$ 1,950.2
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		5,522.6		5,075.6
Assets measured at NAV	[1]	2,378.7		1,950.2
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value Investments		3,143.9		3,125.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value Investments		504.6		589
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value Investments		2,639.3		2,536.4
US Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	136.7		192.7
US Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	136.6		192.7
US Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0.1		0
Non US Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		40	[2]	74.1
Non US Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	40		73.5
Non US Equity Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	0		0.6
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	452		1,271.1
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0		0
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	452		1,271.1
Non-US government securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	130		93.4
Non-US government securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	0		5.3
Non-US government securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	130		88.1
US Corporate Bonds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	1,515.4		616.9
US Corporate Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	92.3		9
US Corporate Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	1,423.1		607.9
Non-US corporate bonds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	373.7		255.2
Non-US corporate bonds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	51.1		6.4
Non-US corporate bonds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	322.6		248.8
Collateralized Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	0.1		2.4
Collateralized Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	0		0
Collateralized Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	0.1		2.4
Other Fixed Income Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[5]	311.4		317.5
Other Fixed Income Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[5]	0		0
Other Fixed Income Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[5]	311.4		317.5
Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[6]	184.6		302.1
Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[6]	184.6		302.1
Short-term Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[6]	0		0
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at NAV	[7]	$ 1,207.6		$ 881.3
[1]	Investments that are measured at NAV (or its equivalent) as a practical expediency have not been classified in the fair value hierarchy.
[2]	Equity securities are comprised of the following investment types: (i) common stock, (ii) preferred stock and (iii) equity exchange traded funds. Level 1 investments in common and preferred stocks and exchange traded funds are valued using quoted market prices multiplied by the number of shares owned.
[3]	U.S. government securities include treasury and agency debt. These investments are valued using broker quotes in an active market.
[4]	The level 1 non-U.S. government securities investment is an exchange traded fund valued using quoted market prices. The level 1 U.S. corporate bonds category is primarily comprised of U.S. dollar denominated investment grade securities and valued using quoted market prices. Level 2 investments are valued utilizing a market approach that includes various valuation techniques and sources such as value generation models, broker quotes in active and non-active markets, benchmark yields and securities, reported trades, issuer spreads, and/or other applicable reference data.
[5]	Other fixed income is comprised of municipal and asset-backed securities. Investments are valued utilizing a market approach that includes various valuation techniques and sources, such as broker quotes in active and non-active markets, benchmark yields and securities, reported trades, issuer spreads and/or other applicable reference data.
[6]	Short-term investments are valued at $1.00/unit, which approximates fair value. Amounts are generally invested in interest-bearing accounts.
[7]	Commingled fund investments are valued at the net asset value per share multiplied by the number of shares held. The determination of net asset value for the commingled funds includes market pricing of the underlying assets as well as broker quotes and other valuation techniques. Commingled funds have been valued using NAV as a practical expedient.We maintain holdings in certain private equity partnerships and private real estate investments for which a liquid secondary market does not exist. The private equity partnerships are commingled investments. Valuation techniques, such as discounted cash flow and market based comparable analyses, are used to determine fair value of the private equity investments. Unobservable inputs used for the discounted cash flow technique include projected future cash flows and the discount rate applied to present value those cash flows. Unobservable inputs used for the market based comparisons technique include EBITDA multiples in other comparable third-party transactions, price to earnings ratios, liquidity, current operating results, as well as input from general partners and other pertinent information. Private equity investments have been valued using NAV as a practical expedient. Private real estate investments are commingled investments. Valuation techniques, such as discounted cash flow and market based comparable analyses, are used to determine fair value of the private equity investments. Unobservable inputs used for the discounted cash flow technique include projected future cash flows and the discount rate applied to present value those cash flows. Unobservable inputs used for the market based comparison technique include a combination of third party appraisals, replacement cost, and comparable market prices. Private real estate investments have been valued using NAV as a practical expedient.Equity related investments are hedged equity investments in a commingled fund that consist primarily of equity indexed investments which are hedged by options and also hold collateral in the form of short term treasury securities. Equity related investments have been valued using NAV as a practical expedient.

Retirement Plans Investments Me

Retirement Plans Investments Measured at NAV (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments		$ 98.8	$ 123.6
Defined Benefit Plans, Fair Value Of Plan Assets		2,378.7	1,950.2
Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	[1]	0	0
Defined Benefit Plans, Fair Value Of Plan Assets	[1]	$ 64.2	$ 265.7
Hedge Funds [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	[1]	91 days	91 days
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	[2]	$ 98.8	$ 123.6
Defined Benefit Plans, Fair Value Of Plan Assets	[2]	$ 1,207.6	$ 881.3
Equity Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	[2]	60 days	60 days
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	[3]	$ 0	$ 0
Defined Benefit Plans, Fair Value Of Plan Assets	[3]	$ 1,106.9	$ 744.1
Fixed Income Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	[3]	10 days	10 days
Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	[4]		$ 0
Defined Benefit Plans, Fair Value Of Plan Assets	[4]		$ 59.1
Other [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	[4]		5 days
[1]	Hedge fund investments are primarily made through shares of limited partnerships or similar structures. Hedge funds are typically valued monthly by third-party administrators that have been appointed by the funds’ general partners. Hedge funds have been valued using NAV as a practical expedient.
[2]	Commingled fund investments are valued at the net asset value per share multiplied by the number of shares held. The determination of net asset value for the commingled funds includes market pricing of the underlying assets as well as broker quotes and other valuation techniques. Commingled funds have been valued using NAV as a practical expedient.We maintain holdings in certain private equity partnerships and private real estate investments for which a liquid secondary market does not exist. The private equity partnerships are commingled investments. Valuation techniques, such as discounted cash flow and market based comparable analyses, are used to determine fair value of the private equity investments. Unobservable inputs used for the discounted cash flow technique include projected future cash flows and the discount rate applied to present value those cash flows. Unobservable inputs used for the market based comparisons technique include EBITDA multiples in other comparable third-party transactions, price to earnings ratios, liquidity, current operating results, as well as input from general partners and other pertinent information. Private equity investments have been valued using NAV as a practical expedient. Private real estate investments are commingled investments. Valuation techniques, such as discounted cash flow and market based comparable analyses, are used to determine fair value of the private equity investments. Unobservable inputs used for the discounted cash flow technique include projected future cash flows and the discount rate applied to present value those cash flows. Unobservable inputs used for the market based comparison technique include a combination of third party appraisals, replacement cost, and comparable market prices. Private real estate investments have been valued using NAV as a practical expedient.Equity related investments are hedged equity investments in a commingled fund that consist primarily of equity indexed investments which are hedged by options and also hold collateral in the form of short term treasury securities. Equity related investments have been valued using NAV as a practical expedient.
[3]	Fixed income and fixed income related instruments consist of commingled debt funds, which are valued at their net asset value per share multiplied by the number of shares held. The determination of net asset value for the commingled funds includes market pricing of the underlying assets as well as broker quotes and other valuation techniques. Commingled debt funds have been valued using NAV as a practical expedient.
[4]	Consists of a global multi-asset investment commingled fund with underlying investments that are diversified across multiple asset classes and include global equity, fixed income securities, commodities and derivative contracts. The commingled fund is valued at its net asset value per share multiplied by the number of shares held. The determination of net asset value for the commingled fund includes market pricing of the underlying assets as well as broker quotes and other valuation techniques. The global multi-asset investment commingled fund has been valued using NAV as a practical expedient.

Retirement Plans Schedule Of Mu

Retirement Plans Schedule Of Multiemployer Plans (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Schedule Of Multiemployer Plans [Line Items]
Percentage of Employees Covered by Collective Bargaining Agreements		43.00%
Percentage of Employees Working Under Expired Collective Bargaining Agreement		24.00%
Percentage of Employees Covered By Collective Bargaining Agreements Expiring in One Year		11.00%
Multiemployer Plan, Withdrawal Obligation		$ 60.1	$ 49
Multiemployer Plan, Accrual Related to a Partial Plan Withdrawal		1.9	2.1	$ 0.7
Pension Plan [Member]
Schedule Of Multiemployer Plans [Line Items]
Multiemployer and Other Plans, Period Contributions	[1]	$ 5.1	$ 4.5	5
Pension Plan [Member] | Pace Industry Union Management Pension Fund [Member]
Schedule Of Multiemployer Plans [Line Items]
Percentage of Employees Covered by Collective Bargaining Agreements		14.00%
Entity Tax Identification Number		116,166,763
Multiemployer Plan Number		1
Multiemployer Plans, Certified Zone Status		Red	Red
Multiemployer Plans, Funding Improvement Plan and Rehabilitation Plan		Implemented
Multiemployer and Other Plans, Period Contributions	[1],[2]	$ 3.5	$ 3.3	$ 3.3
Multiemployer Plans, Surcharge		Yes
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date, First		Jun. 1, 2017
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date, Last		Jun. 25, 2023
Contributions Exceed 5% of Total Plan Contributions			Yes	Yes
Pension Plan [Member] | Other Funds [Member]
Schedule Of Multiemployer Plans [Line Items]
Multiemployer and Other Plans, Period Contributions	[1],[3]	$ 1.6	$ 1.2	$ 1.7
Minimum [Member]
Schedule Of Multiemployer Plans [Line Items]
Multiemployer Plans, Withdrawal Obligation if Company Withdraws from All MEPPs		140
Maximum [Member]
Schedule Of Multiemployer Plans [Line Items]
Multiemployer Plans, Withdrawal Obligation if Company Withdraws from All MEPPs		$ 200
[1]	Contributions represent the amounts contributed to the plan during the fiscal year.
[2]	Our contributions for fiscal 2016 and 2015 exceeded 5% of total plan contributions. Although the plan data for fiscal 2017 is not yet available, we would expect to continue to exceed 5% of total plan contributions.
[3]	Two additional MEPPs in which we participate have been certified in the red zone for critical and declining.

Retirement Plans Defined Contri

Retirement Plans Defined Contribution and Supplemental Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Defined Contribution Plan Disclosure [Line Items]
Defined Contribution Plan Employer Contribution on Basic Salary, Employees Covered under a CBA, Maximum, Low End of Range	3.00%
Defined Contribution Plan Employer Contribution on Basic Salary, Employees Covered under a CBA, Maximum, High End of Range	4.00%
Defined Contribution Plan Employer Contribution on Basic Salary, Maximum, High End of Range	7.50%
Defined Contribution Plan Employer Contribution on Basic Salary, Maximum Matching Contribution	5.00%
Defined Contribution Plan Employer Contribution on Basic Salary, Automatic Matching Contribution	2.50%
Defined Contribution Plan, Cost	$ 104.1	$ 86.5	$ 36.6

Shareholders' Equity (Details)

Shareholders' Equity (Details) - USD ($) shares in Millions, $ in Millions		Jul. 01, 2015	Sep. 30, 2015	Dec. 31, 2014	[1]	Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2015
Purchases of Common Stock Excluding Merger Related Purchases						$ 93		$ 335.3		$ 336.7
Treasury Stock, Value, Acquired, Par Value Method			$ 328	$ 8.7
Common Stock [Member]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased		40
Purchases of common stock			5.4	0.2		1.8	[1]	8.1	[1]	16.1	[1]
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased						24.7
MeadWestvaco [Member]
Purchases of Common Stock Excluding Merger Related Purchases	[1]	$ 667.8
MeadWestvaco [Member] | Common Stock [Member]
Purchases of common stock	[1]	10.5
[1]	In fiscal 2017, we repurchased approximately 1.8 million shares of our Common Stock for an aggregate cost of $93.0 million. In fiscal 2016, we repurchased approximately 8.1 million shares of our Common Stock for an aggregate cost of $335.3 million. Pursuant to the then existing repurchase plan, in the first quarter of fiscal 2015, RockTenn repurchased 0.2 million shares for an aggregate cost of $8.7 million. Subsequent to the Combination, in the fourth quarter of fiscal 2015, we repurchased approximately 5.4 million shares of our Common Stock for an aggregate cost of $328.0 million under the new authorization. Separately as part of the Combination, we repurchased 10.5 million shares of our Common Stock for an aggregate cost of $667.8 million.

Share-Based Compensation (Detai

Share-Based Compensation (Details) $ / shares in Units, $ in Millions		Jun. 06, 2017USD ($)$ / sharesshares	Jul. 01, 2015USD ($)shares	Sep. 30, 2017USD ($)$ / sharesshares	Sep. 30, 2016USD ($)$ / sharesshares	Sep. 30, 2015USD ($)$ / sharesshares	May 15, 2016	Feb. 02, 2016shares	May 27, 2011shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Stock Appreciation Rights, Exercises in Period, Intrinsic Value | $				$ 0.4	$ 0.2
Share-based Compensation Arrangement by Share-based Payment Award, Spin-off Adjustment, Conversion Factor							1.12
Allocated Share-based Compensation Expense | $				60.9	75.7	$ 49.2
Share-based Compensation Expense Included in the Gain on Sale of HH&B | $				2.9
Reduction of Share-based Compensation Expense Related to the Rescission of Shares Granted in Excess of Plan Limits | $				5.4
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense | $				$ 22.5	$ 29.2	$ 19
Expected term (in years)					7 years	3 years 11 months
Expected volatility					38.30%	21.90%
Risk-free rate					1.60%	2.40%
Expected dividends					4.50%	1.30%
Stock Options [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				3 years
Fair value of share-based awards issued in the acquisition | $				$ 1.9	$ 0	$ 210.9
Excess tax benefits from share-based compensation | $				6.7	0.3	23
Proceeds from Stock Options Exercised | $				$ 59.2	$ 33.9	$ 27.2
Stock Appreciation Rights (SARs) [Member]
Stock Options [Roll Forward]
Shares outstanding, beginning of fiscal year				65,971
Shares exercised				(13,868)
Shares expired				(1,087)
Shares outstanding, end of fiscal year				51,016	65,971
Weighted Average Exercise Price, outstanding, beginning of period | $ / shares				$ 26.07
Weighted Average Exercise Price, shares exercised | $ / shares				28.43
Weighted Average Exercise Price, shares expired | $ / shares				31.87
Weighted Average Exercise Price, outstanding, end of period | $ / shares				$ 25.30	$ 26.07
Aggregate Intrinsic Value, Outstanding at end of period | $				$ 1.6
Aggregate Intrinsic Value, Exercisable at end of period | $				$ 1.6
Shares, Exercisable at end of period				51,016
Weighted Average Exercise Price, exercisable at end of period | $ / shares				$ 25.30
Weighted Average Remaining Contractual Term, Outstanding at end of period				2 years 10 months
Weighted Average Remaining Contractual Term, Exercisable				2 years 10 months
Restricted Stock with Service Condition Assumed in Purchase Accounting [Member]
Stock Options [Roll Forward]
Granted	[1]				0
Restricted Stock with Service Condition [Member]
Stock Options [Roll Forward]
Granted	[2]			309,850	27,370	86,265
Restricted Stock, Target Awards [Member]
Stock Options [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				3 years
Restricted Stock, Total Shareholder Return Grant, 2017 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)				2 years 11 months
Expected volatility				30.60%
Risk-free rate				1.40%
Stock Options [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares				$ 64.41
Stock Options [Member]
Stock Options [Roll Forward]
Shares outstanding, beginning of fiscal year				8,065,816
Shares exercised				(2,074,828)
Shares expired				(57,225)
Shares forfeited				(67,636)
Shares outstanding, end of fiscal year				5,866,127	8,065,816
Weighted Average Exercise Price, outstanding, beginning of period | $ / shares				$ 29.73
Weighted Average Exercise Price, shares exercised | $ / shares				27.38
Weighted Average Exercise Price, shares expired | $ / shares				32.61
Weighted Average Exercise Price, shares forfeited | $ / shares				31.50
Weighted Average Exercise Price, outstanding, end of period | $ / shares				$ 30.51	$ 29.73
Aggregate Intrinsic Value, Outstanding at end of period | $				$ 154.6
Aggregate Intrinsic Value, Exercisable at end of period | $				$ 131.5
Shares, Exercisable at end of period				4,883,459
Weighted Average Exercise Price, exercisable at end of period | $ / shares				$ 29.94
Weighted Average Remaining Contractual Term, Outstanding at end of period				4 years 7 months
Weighted Average Remaining Contractual Term, Exercisable				4 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number				5,853,074
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price | $ / shares				$ 30.50
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Remaining Contractual Term				4 years 7 months
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value | $				$ 154.2
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares					$ 8.06	$ 28.78
Aggregate intrinsic value of options exercised | $				$ 54.3	$ 14.5	$ 25.1
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				3 years
Share-based Compensation Arrangement by Share-based Payment Award, Contractual Term, Maximum				10 years
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized | $				$ 2.4
Restricted Stock [Member]
Stock Options [Roll Forward]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized | $				$ 83.5
Granted				1,605,113	1,750,546	2,324,862
Weighted Average Grant Date Fair Value, Granted | $ / shares				$ 53.79
MPS [Member]
Stock Options [Roll Forward]
Ratio of MPS Shares to WestRock Shares		33.00%
Weighted Average Grant Date Fair Value, Granted | $ / shares		$ 54.24
Fair value of share-based awards issued in business combinations | $		$ 1.9
MPS [Member] | Restricted Stock with Service Condition Assumed in Purchase Accounting [Member]
Stock Options [Roll Forward]
Granted	[1]	119,373
MeadWestvaco [Member]
Stock Options [Roll Forward]
Fair value of share-based awards issued in the acquisition | $			$ 210.9
Ratio of MeadWestvaco Shares to WestRock Shares			78.00%
MeadWestvaco [Member] | Restricted Stock with Service Condition Assumed in Purchase Accounting [Member]
Stock Options [Roll Forward]
Granted	[1]		327,005
WestRock 2016 Incentive Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized								9,600,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant				6,900,000
WestRock 2016 Incentive Stock Plan [Member] | Restricted Stock Target Awards Potentially Issuable [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant				2,000,000
RockTenn 2004 Incentive Stock Plan, as Amended [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized				15,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant				3,100,000
RockTenn 2004 Incentive Stock Plan, as Amended [Member] | Restricted Stock Target Awards Potentially Issuable [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant				400,000
MWV 2005 Performance Incentive Plan, as Amended [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized			12,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant				8,900,000
MWV 2005 Performance Incentive Plan, as Amended [Member] | Restricted Stock Target Awards Potentially Issuable [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant				100,000
Smurfit-Stone Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized									7,900,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant				5,900,000
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date				15.00%
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant				2,600,000				2,500,000
[1]	These shares vest over approximately one to three years.
[2]	These shares vest over approximately three to four years.

Share-Based Compensation Restri

Share-Based Compensation Restricted Stock (Details) - USD ($) $ / shares in Units, $ in Millions		Jun. 06, 2017	Jul. 01, 2015	Sep. 30, 2017		Sep. 30, 2016	Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Excess tax benefits from share-based compensation				$ 6.7		$ 0.3	$ 23
Number of Target Shares Related to Rescission of Shares Granted in Excess of Plan Limits				50,326
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				3 years
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				3 years
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized				$ 2.4
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition				1 year 1 month
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Performance Based Awards Reflected				100.00%
Additional Shares Expected to Be Issued Based on Current Projection of Performance Target Levels				1,400,000
Unvested, beginning of fiscal year				2,704,904
Granted				1,605,113		1,750,546	2,324,862
Vested				(1,112,909)		(1,589,761)	(1,725,435)
Forfeited				(237,659)
Unvested, end of fiscal year				2,959,449	[1]	2,704,904
Unvested, Weighted Average Grant Date Fair Value, beginning of period				$ 40.89
Weighted Average Grant Date Fair Value, Granted				53.79
Weighted Average Grant Date Fair Value, Vested				48.07
Weighted Average Grant Date Fair Value, Forfeited				39.69
Unvested, Weighted Average Grant Date Fair Value, end of period				$ 45.28	[1]	$ 40.89
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized				$ 83.5
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition				1 year 7 months
Aggregate fair value of vested restricted stock				$ 59.5		$ 57.5	$ 110.4
Restricted Stock, Non-Employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				1 year
Granted	[2]			26,521		64,155	15,255
Restricted Stock, Attainment of Performance Condition in Excess of Target
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	[3]			340,319			801,810
Restricted Stock, Attainment of Performance Condition in Excess of Target [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	[3]					447,261
Restricted Stock, Service Condition and Cash Flow per Share Performance Condition at Target [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	[4]			507,070		1,211,760	379,519	[5]
Restricted Stock, Target Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Award Based on Level of Performance Attained, Maximum				200.00%
Percentage of Award Based on Level of Performance Attained, Minimum				0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				3 years
Restricted Stock, Service Condition and Relative Total Shareholder Return Market Condition at Target [Member] [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	[4]			301,980		0	0
Restricted Stock, Service Condition and Performance Condition at Target [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	[6],[7]			0		0
Restricted Stock with Service Condition Assumed in Purchase Accounting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	[7]					0
Restricted Stock, Target Awards, 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Awarded Based on Performance Level Achieved				176.60%
Restricted Stock, Target Awards, 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Awarded Based on Performance Level Achieved						200.00%
Restricted Stock, Target Awards, 2012 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Awarded Based on Performance Level Achieved							200.00%
Restricted Stock with Service Condition [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	[8]			309,850		27,370	86,265
Fiscal 2015 Grant Prorated Upon Combination [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Awarded Based on Performance Level Achieved			146.50%
Granted	[9]			0		0	64,323
Proration Factor Applied to Grant Upon Combination			16.60%
MeadWestvaco [Member] | Restricted Stock, Service Condition and Performance Condition at Target [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	[6],[7]		650,685
MeadWestvaco [Member] | Restricted Stock with Service Condition Assumed in Purchase Accounting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	[7]		327,005
MPS [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Average Grant Date Fair Value, Granted		$ 54.24
MPS [Member] | Restricted Stock with Service Condition Assumed in Purchase Accounting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	[7]	119,373
Minimum [Member] | Restricted Stock Accelerated in Connection with the Combination [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Awarded Based on Performance Level Achieved				146.50%		146.50%
Minimum [Member] | Restricted Stock with Service Condition Assumed in Purchase Accounting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				1 year
Minimum [Member] | Restricted Stock with Service Condition [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				3 years
Minimum [Member] | MeadWestvaco [Member] | Restricted Stock, Service Condition and Performance Condition at Target [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Awarded Based on Performance Level Achieved			100.00%
Maximum [Member] | Restricted Stock Accelerated in Connection with the Combination [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Awarded Based on Performance Level Achieved				200.00%		200.00%
Maximum [Member] | Restricted Stock with Service Condition Assumed in Purchase Accounting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				3 years
Maximum [Member] | Restricted Stock with Service Condition [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				4 years
Maximum [Member] | MeadWestvaco [Member] | Restricted Stock, Service Condition and Performance Condition at Target [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of Awarded Based on Performance Level Achieved			168.00%
RockTenn 2004 Incentive Stock Plan, as Amended [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant				3,100,000
RockTenn 2004 Incentive Stock Plan, as Amended [Member] | Restricted Stock Target Awards Potentially Issuable [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant				400,000
[1]	Target awards granted with a performance condition, net of subsequent forfeitures, may be increased up to 200% of the target or decreased to zero, subject to the level of performance attained. The awards are reflected in the table at the target award amount of 100%. Based on current facts and assumptions we are forecasting the performance of the grants to be attained at levels that would result in the issuance of approximately 1.4 million additional shares. However, it is possible that the performance attained may vary.
[2]	Non-employee director grants generally vest over a period of up to one year and are deemed issued on the grant date and have voting and dividend rights.
[3]	Shares granted in the table above include shares subsequently issued for the level of performance attained in excess of target. Shares issued in fiscal 2017 for the fiscal 2014 Cash Flow to Equity Ratio were at 176.6% of target. Shares issued in fiscal 2016 for the fiscal 2013 Cash Flow to Equity Ratio were at 200% of target. Shares issued in fiscal 2015 for the fiscal 2012 Cash Flow to Equity Ratio were at 200% of target. Shares issued in fiscal 2017, 2016 and 2015 also include shares accelerated for terminated employees primarily as a result of the Combination, which were achieved at between 146.5% and 200% of target.
[4]	These employee grants vest over approximately three years and have adjustable ranges from 0-200% of target subject to the level of performance attained in the respective award agreement. The employee grants with a relative Total Shareholder Return condition were valued using a Monte Carlo simulation, the terms of which are outlined below.
[5]	Shares granted in fiscal 2015 were reduced by 50,326 shares at target related to the rescission of shares granted to our CEO that were inadvertently granted in excess of plan limits.
[6]	The performance period applicable to each award ended upon consummation of the Combination, and the performance goals were determined in accordance with the applicable grant letter to be attained at between 100% and 168% of target.
[7]	These shares vest over approximately one to three years.
[8]	These shares vest over approximately three to four years.
[9]	As a result of the Combination, certain target awards granted to employees in fiscal 2015 were prorated with the employee receiving approximately 16.6% of the target award in accordance with the terms in the award document prior to the application of the performance adjustment. The performance period applicable to each award ended upon consummation of the Combination, and the performance goals were determined in accordance with the applicable grant letter to be attained at 146.5% of target.

Share-Based Compensation Employ

Share-Based Compensation Employee Stock Purchase Plan (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Feb. 02, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 58	$ 75.7	$ 49.2
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date	15.00%
Stock Issued During Period, Shares, Employee Stock Purchase Plans	0.2	0.1	0.1
Share-based compensation expense	$ 1.3	$ 0.4	$ 0.5
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	2.6			2.5

Related Party Transactions (Det

Related Party Transactions (Details) - Affiliated Entity [Member] - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Related Party Transaction [Line Items]
Net sales to affiliated companies	$ 423.6	$ 346.6	$ 342.8
Accounts receivable due from affiliated companies	$ 65.1	$ 59.4

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	Sep. 30, 2017USD ($)
Commitments and Contingencies [Line Items]
Accrual for Environmental Loss Contingencies	$ 15
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 50
Number of Lawsiuts the Company Has Been Named a Defendant in Asbestos-related Personal Injury Litigation	725
Guarantor Obligations, Current Carrying Value	$ 11.9
Other Long Term Liabilities [Member]
Commitments and Contingencies [Line Items]
Accrual for Environmental Loss Contingencies	9.6
Other Current Liabilities [Member]
Commitments and Contingencies [Line Items]
Accrual for Environmental Loss Contingencies	5.4
Capital Addition Purchase Commitments [Member]
Commitments and Contingencies [Line Items]
Long-term Purchase Commitment, Estimated Amount	$ 155

Special Purpose Entities (Detai

Special Purpose Entities (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Dec. 06, 2013	Dec. 31, 2007
Debt Instrument [Line Items]
Restricted assets held by special purpose entities	$ 1,287.4	$ 1,293.8
Non-recourse liabilities held by special purpose entities	$ 1,161.9	$ 1,170.2
Installment Note [Member]
Debt Instrument [Line Items]
Notes Receivable Interest Rate	5.207%
MeadWestvaco [Member] | Timber Note [Member]
Debt Instrument [Line Items]
Restricted assets held by special purpose entities	$ 363			$ 398
MeadWestvaco [Member] | Installment Note [Member]
Debt Instrument [Line Items]
Restricted assets held by special purpose entities	924.4		$ 860
MeadWestvaco [Member] | Secured Financing Liability, Maturity in December 2023 [Member]
Debt Instrument [Line Items]
Non-recourse liabilities held by special purpose entities	840.2		$ 774
MeadWestvaco [Member] | Secured Financing Liability, Maturity in October 2027 [Member]
Debt Instrument [Line Items]
Non-recourse liabilities held by special purpose entities	$ 321.7			$ 338.3

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Millions	Sep. 21, 2016	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Apr. 01, 2017	Apr. 01, 2016	Sep. 30, 2014
Segment Reporting Information [Line Items]
Net sales		$ 4,060.6	$ 3,695.6	$ 3,656.3	$ 3,447.2	$ 3,611.7	$ 3,596.5	$ 3,492.7	$ 3,470.9	$ 14,859.7	$ 14,171.8	$ 11,124.8
Pension risk transfer expense	$ (370.7)					(370.7)	0	0	0	0	(370.7)	0
Pension lump sum settlement expense		(3.9)	0	(28.7)	0				(20)	(32.6)	0	(11.5)
Land and Development impairment		4	0	42.7	0					46.7	0	0
Restructuring and other costs, net		(38)	(59.4)	(18.3)	(81)	(49.4)	(43.1)	(111.1)	(162.8)	(196.7)	(366.4)	(140.8)
Interest expense										(277.7)	(256.7)	(132.5)
Gain (loss) on extinguishment of debt		(0.1)	2	(0.1)	0	2.7	$ 0	$ 0	$ 0	1.8	2.7	(2.6)
Interest income and other income (expense), net										66.7	58.6	9.7
Gain on sale of HH&B		2.2	$ 190.6	$ 0	$ 0					192.8	0	0
Income from continuing operations before income taxes										857.6	244.6	734.2
Pre-Tax Inventory Step-Up										26.5	8.1	64.7
Identifiable assets		25,089				23,038.2				25,089	23,038.2	25,372.4
Goodwill		5,528.3				4,778.1				5,528.3	4,778.1
Depreciation, depletion and amortization										1,116.6	1,146.5	740.8
Capital expenditures										778.6	796.7	585.5
Equity Method Investments		360.6				328.9				360.6	328.9	60.2
Land and Development [Member]
Segment Reporting Information [Line Items]
Identifiable assets		89.8				460.6				89.8	460.6	545.5
Depreciation, depletion and amortization										0.7	1.4	0.2
Equity Method Investments		14.4				28.6				14.4	28.6	31
Corrugated Packaging [Member]
Segment Reporting Information [Line Items]
Pre-Tax Inventory Step-Up										1.4	3.4	2.2
Identifiable assets		10,537.7				10,046				10,537.7	10,046	9,467.3
Goodwill		1,865.7				1,722.5				1,865.7	1,722.5	1,667.5			$ 1,525.4
Depreciation, depletion and amortization										597.9	576.2	496.6
Capital expenditures										492.1	490.1	378.4
Equity Method Investments		321.1				281.2				321.1	281.2	7.9
Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Identifiable assets		0				0				0	0	2,618.5
Depreciation, depletion and amortization										0	57.2	22
Capital expenditures										0	45.2	28.6
Operating Segments [Member]
Segment Reporting Information [Line Items]
Goodwill		5,528.3				4,778.1				5,528.3	4,778.1	4,647.1			1,926.4
Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Identifiable assets		173.6				52.3				173.6	52.3	10.2
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Identifiable assets		2,410.1				2,356.8				2,410.1	2,356.8	2,555.2
Depreciation, depletion and amortization										9.8	12.8	20.2
Capital expenditures										20.7	16.5	12.4
Equity Method Investments		0.4				(3.1)				0.4	(3.1)	0
Consumer Packaging [Member]
Segment Reporting Information [Line Items]
Pre-Tax Inventory Step-Up										25.1	4.7	62.5
Identifiable assets		11,877.8				10,122.5				11,877.8	10,122.5	10,175.7
Goodwill		3,662.6				3,055.6				3,662.6	3,055.6	2,979.6			$ 401
Depreciation, depletion and amortization										508.2	498.9	201.8
Capital expenditures										265.8	244.9	166.1
Equity Method Investments		24.7				22.2				24.7	22.2	21.3
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues										15,104.6	14,376.4	11,302
Net sales										14,859.7	14,171.8	11,124.8
Segment income (loss)										1,193.5	1,226.2	1,070.3
Operating Segments [Member] | Land and Development [Member]
Segment Reporting Information [Line Items]
Revenues										243.8	119.8	45
Net sales										243.8	119.8	45
Segment income (loss)										13.8	4.6	(3.4)
Operating Segments [Member] | Corrugated Packaging [Member]
Segment Reporting Information [Line Items]
Revenues										8,408.3	7,868.5	7,516.9
Net sales										8,252.5	7,732.3	7,386.3
Segment income (loss)										753.9	739.9	806.7
Operating Segments [Member] | Consumer Packaging [Member]
Segment Reporting Information [Line Items]
Revenues										6,452.5	6,388.1	3,740.1
Net sales										6,363.4	6,319.7	3,693.5
Segment income (loss)										425.8	481.7	267
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues										244.9	204.6	177.2
Intersegment Eliminations [Member] | Corrugated Packaging [Member]
Segment Reporting Information [Line Items]
Revenues										155.8	136.2	130.6
Intersegment Eliminations [Member] | Consumer Packaging [Member]
Segment Reporting Information [Line Items]
Revenues										89.1	68.4	46.6
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Pension risk transfer expense										0	(370.7)	0
Pension lump sum settlement expense										(32.6)	0	(11.5)
Land and Development impairment										(46.7)	0	0
Non-allocated expenses										(43.5)	(49.1)	(58.4)
Interest expense										(277.7)	(256.7)	(132.5)
Gain (loss) on extinguishment of debt										1.8	2.7	(2.6)
Interest income and other income (expense), net										66.7	58.6	9.7
Gain on sale of HH&B										192.8	0	$ 0
Grupo Gondi Investment [Member]
Segment Reporting Information [Line Items]
Equity Method Investments														$ 300
Equity Method Investment, Ownership Percentage														25.00%
Grupo Gondi Investment [Member] | Corrugated Packaging [Member]
Segment Reporting Information [Line Items]
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity		76.2				65.3				76.2	65.3
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity, Amortizable Portion		$ 59.2				$ 56.2				$ 59.2	$ 56.2
Equity Method Investment, Ownership Percentage													27.00%
Minimum [Member] | Grupo Gondi Investment [Member] | Corrugated Packaging [Member]
Segment Reporting Information [Line Items]
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity, Lives of Underlying Assets											10 years
Maximum [Member] | Grupo Gondi Investment [Member] | Corrugated Packaging [Member]
Segment Reporting Information [Line Items]
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity, Lives of Underlying Assets											15 years

Segment Information Segment Inf

Segment Information Segment Information, Geographical Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Revenues from External Customers, Segment Income and Long-Lived Assets [Line Items]
Net sales	$ 4,060.6	$ 3,695.6	$ 3,656.3	$ 3,447.2	$ 3,611.7	$ 3,596.5	$ 3,492.7	$ 3,470.9	$ 14,859.7	$ 14,171.8	$ 11,124.8
Foreign Operations [Member]
Revenues from External Customers, Segment Income and Long-Lived Assets [Line Items]
Net sales									2,621.2	2,426.6	1,506.5
Segment income (loss)									260.1	226.1	171.6
Long-Lived Assets	$ 1,558.3				$ 1,341.5				$ 1,558.3	$ 1,341.5	$ 1,228
Percentage of Net Sales to Unaffiliated Customers									17.60%	17.10%	13.50%
Percentage of Segment Income									21.80%	18.40%	16.00%
Percentage of Long-Lived Assets	17.10%				14.40%				17.10%	14.40%	13.40%

Segment Information Changes in

Segment Information Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Goodwill [Roll Forward]
Goodwill, beginning of fiscal year	$ 4,778.1
Goodwill, end of fiscal year	5,528.3	$ 4,778.1
Operating Segments [Member]
Goodwill [Roll Forward]
Goodwill, Gross beginning of fiscal year	4,820.9	4,689.9	$ 1,969.2
Accumulated impairment losses, beginning of period	(42.8)	(42.8)	(42.8)
Goodwill, beginning of fiscal year	4,778.1	4,647.1	1,926.4
Goodwill acquired	1,045.4	60.4	2,769.8
Goodwill disposed of	(329.6)	(24)
Purchase price allocation adjustments	8.1	62.7	1.3
Translation adjustment	26.3	31.9	(50.4)
Goodwill, Gross end of fiscal year	5,571.1	4,820.9	4,689.9
Accumulated impairment losses, end of period	(42.8)	(42.8)	(42.8)
Goodwill, end of fiscal year	5,528.3	4,778.1	4,647.1
Corrugated Packaging [Member]
Goodwill [Roll Forward]
Goodwill, Gross beginning of fiscal year	1,722.5	1,667.5	1,525.4
Accumulated impairment losses, beginning of period	0	0	0
Goodwill, beginning of fiscal year	1,722.5	1,667.5	1,525.4
Goodwill acquired	137.6	52.4	183.3
Goodwill disposed of	0	(24)
Purchase price allocation adjustments	(1.2)	(4.9)	2.4
Translation adjustment	6.8	31.5	(43.6)
Goodwill, Gross end of fiscal year	1,865.7	1,722.5	1,667.5
Accumulated impairment losses, end of period	0	0	0
Goodwill, end of fiscal year	1,865.7	1,722.5	1,667.5
Consumer Packaging [Member]
Goodwill [Roll Forward]
Goodwill, Gross beginning of fiscal year	3,098.4	3,022.4	443.8
Accumulated impairment losses, beginning of period	(42.8)	(42.8)	(42.8)
Goodwill, beginning of fiscal year	3,055.6	2,979.6	401
Goodwill acquired	907.8	8	2,586.5
Goodwill disposed of	(329.6)	0
Purchase price allocation adjustments	9.3	67.6	(1.1)
Translation adjustment	19.5	0.4	(6.8)
Goodwill, Gross end of fiscal year	3,705.4	3,098.4	3,022.4
Accumulated impairment losses, end of period	(42.8)	(42.8)	(42.8)
Goodwill, end of fiscal year	$ 3,662.6	$ 3,055.6	$ 2,979.6

Financial Results by Quarter100

Financial Results by Quarter (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	Sep. 21, 2016	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jun. 30, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Effective Income Tax Rate Reconciliation, Release of State Deferred Tax Liability as a Result of Equity Restructuring, Amount					$ 23.8
Net sales		$ 4,060.6	$ 3,695.6	$ 3,656.3	3,447.2	$ 3,611.7	$ 3,596.5	$ 3,492.7	$ 3,470.9			$ 14,859.7	$ 14,171.8	$ 11,124.8
Gross profit		778	695.5	675.4	591.3	719.3	727.3	657.3	654.7			2,740.2	2,758.6	2,138.3
Pension lump sum settlement and retiree medical curtailment, net		3.9	0	28.7	0				20			32.6	0	11.5
Pension risk transfer expense	$ 370.7					370.7	0	0	0			0	370.7	0
Land and Development impairment		4	0	42.7	0							46.7	0	0
Land and Development Impairment, Net of Noncontrolling Interest				36.3
Land and Development Impairment, Noncontrolling Interest				6.4
Restructuring and other costs, net		38	59.4	18.3	81	49.4	43.1	111.1	162.8			196.7	366.4	140.8
Gain (loss) on extinguishment of debt		(0.1)	2	(0.1)	0	2.7	0	0	0			1.8	2.7	(2.6)
Gain on sale of HH&B		2.2	190.6	0	0							192.8	0	0
Income (loss) from continuing operations						(86.4)	152.4	58.4	30.4			698.6	154.8	501.2
(Loss) income from discontinued operations (net of income tax benefit (expense) of $0, $32.3 and $(17.5)						(5.3)	(58.7)	1.4	(482.1)			0	(544.7)	10.6
Consolidated net income (loss)		195.3	326.6	98.2	78.5	(91.7)	93.7	59.8	(451.7)			698.6	(389.9)	511.8
Net income (loss) attributable to common stockholders		$ 196.1	$ 328.1	$ 103.1	$ 80.9	$ (92)	$ 92.3	$ 56.9	$ (453.5)			$ 708.2	$ (396.3)	$ 507.1
Basic earnings per share from continuing operations						$ (0.34)	$ 0.60	$ 0.22	$ 0.12			$ 2.81	$ 0.60	$ 2.92
Diluted earnings per share from continuing operations						(0.34)	0.59	0.22	0.12			2.77	0.59	2.87
Basic earnings (loss) per share attributable to common stockholders		$ 0.77	$ 1.29	$ 0.40	$ 0.32	(0.37)	0.37	0.22	(1.76)			2.81	(1.56)	2.97
Diluted earnings (loss) per share attributable to common stockholders		$ 0.76	1.29	0.40	0.32	(0.37)	0.36	$ 0.22	(1.73)			$ 2.77	$ (1.54)	$ 2.93
Plan Assets Used to Settle Pension Obligations Plan by Purchasing Group Annuity Contracts from Prudential	$ 2,500
Basic Earnings Per Share, Estimated Increase (Decrease) Due to Specific Items Occurring During Quarter			0.76						(1.86)
Diluted Earnings Per Share, Estimated Increase (Decrease) Due to Specific Items Occurring During Quarter			$ 0.75						$ (1.83)
Basic and Diluted Earnings Per Share from Continuing Operations and Basic and Diluted Earnings Per Share, Estimated Increase (Decrease) Due to Specific Items Occurring During Quarter						$ (0.91)
Pre-Tax Inventory Step-Up												$ 26.5	$ 8.1	$ 64.7
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions												25.6	9.7	3.7
Basic and Diluted Earnings Per Share, Estimated Increase (Decrease) Due to Specific Items Occurring During Quarter				$ (0.16)	$ 0.09		$ (0.27)
Corrugated Packaging [Member]
Pre-Tax Inventory Step-Up												1.4	3.4	2.2
Consumer Packaging [Member]
Pre-Tax Inventory Step-Up												25.1	4.7	62.5
Other Postretirement Benefits Plan [Member]
Pension lump sum settlement and retiree medical curtailment, net										$ 8.1	$ 8.5
Defined Benefit Plan, Recognized Net (Gain) Loss Due to Curtailments												$ (0.3)	0	(8.5)
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member] | Specialty Chemicals Business [Member]
(Loss) income from discontinued operations (net of income tax benefit (expense) of $0, $32.3 and $(17.5)													$ (544.7)	$ 10.6
Goodwill, Impairment Loss									$ 478.3
Customer Lists [Member] | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member] | Specialty Chemicals Business [Member]
Impairment of Intangible Assets (Excluding Goodwill)							$ 101.1

Subsequent Event (Details)

Subsequent Event (Details) $ in Millions	Nov. 16, 2017USD ($)T	Oct. 31, 2017USD ($)	Oct. 20, 2017USD ($)	Aug. 24, 2017USD ($)	Jun. 22, 2016USD ($)	Apr. 01, 2016USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)	Jul. 01, 2015USD ($)
Subsequent Event [Line Items]
Additions to debt							$ 742.6	$ 1,511.8	$ 2,176.3
Grupo Gondi Investment [Member]
Subsequent Event [Line Items]
Equity Method Investment, Ownership Percentage						25.00%
Payments to Acquire Interest in Joint Venture						$ 175
Subsequent Event [Member]
Subsequent Event [Line Items]
Aggregate Principal Amount of Short-term Unsecured Commercial Paper Program, Maximum		$ 1,000
Investment over Two Years in Connection with Installing Kraft Linerboard Machine and Related Infrastructure at Florence, SC Mill	$ 410
Expected Investment Over Next Five Years to Support New Kraft Linerboard Machine and Other Projects at Florence, SC Mill	$ 60
Expected Additional Production Attributable to New Kraft Linerboard Machine | T	710,000
Subsequent Event [Member] | Grupo Gondi Investment [Member]
Subsequent Event [Line Items]
Equity Method Investment, Ownership Percentage			32.30%
Payments to Acquire Interest in Joint Venture			$ 108
Unsecured Debt [Member] | Subsequent Event [Member] | Wells Fargo Bank, NA Credit Facility [Member]
Subsequent Event [Line Items]
Credit Facility, maximum borrowing capacity		450
Secured Debt [Member] | Subsequent Event [Member] | Receivables Facility [Member]
Subsequent Event [Line Items]
Additions to debt		485
Unsecured Debt [Member] | Term Loan Facility [Member]
Subsequent Event [Line Items]
Credit Facility, maximum borrowing capacity										$ 2,300
Prepayment of Amortization Payments				$ 575	$ 200
Unsecured Debt [Member] | Subsequent Event [Member] | Term Loan Facility [Member]
Subsequent Event [Line Items]
Prepayment of Amortization Payments		$ 485