Consolidated Statements of Income and Comprehensive Income - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Net sales		$ 1,690.6	$ 1,536.5
Cost of sales		(1,334.5)	(1,198.3)
Gross profit		356.1	338.2
Selling, general and administrative expenses		(134.9)	(127.8)
Other expense, net		(8.3)	(7.0)
Income from operations	[1]	212.9	203.4
Interest expense, net and other	[1]	(26.3)	(24.3)
Income before taxes	[1]	186.6	179.1
Provision for income taxes		(46.5)	(61.7)
Net income		$ 140.1	$ 117.4
Net income per common share:
Basic		$ 1.48	$ 1.25
Diluted		1.48	1.24
Dividends declared per common share		$ 0.63	$ 0.63
Statements of Comprehensive Income:
Net income		$ 140.1	$ 117.4
Foreign currency translation adjustment		(0.1)	(0.2)
Reclassification adjustments to cash flow hedges included in net income, net of tax of $0.4 million and $0.5 million		1.0	0.9
Amortization of pension and postretirement plans actuarial loss and prior service cost, net of tax of $1.0 million and $1.2 million		3.0	2.2
Other comprehensive income		3.9	2.9
Comprehensive income		$ 144.0	$ 120.3

[1] (a)Effective January 1, 2018, the Company adopted ASU 2017-07, Compensation: Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost and applied this standard retrospectively to the prior period reflected herein. This new standard requires the presentation of non-service cost components of net periodic benefits expense to be shown separately outside the subtotal of operating income in the income statement. See Note 2, New and Recently Adopted Accounting Standards, for more information. The components of our financial statements affected by the change in presentation of operating and non-operating pension expense as originally reported in 2017 and as adjusted for the requirements per the new standard are as follows (dollars in millions): Segment income (loss) March 31, 2017 As Reported Non-Operating Pension Adjustment March 31, 2017 Adjusted Packaging $190.8 $1.7 $192.5 Paper 29.8 (1.9) 27.9 Corporate (17.5) 0.5 (17.0) Income from operations 203.1 0.3 203.4 Interest expense, net and other (24.0) (0.3) (24.3) Income before taxes $179.1 $— $179.1