Consolidated Statements of Income and Comprehensive Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Reclassification adjustments to cash flow hedges included in net income, tax	$ 2.2	$ 2.2	$ 2.2
Amortization of pension and postretirement plans actuarial loss and prior service cost, tax	4.9	4.2	5.6
Changes in unfunded employee benefit obligations, tax	$ 18.0	$ 15.7	$ (8.9)

Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e640-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph c
-URI http://asc.fasb.org/extlink&oid=84234895&loc=d3e41638-113959

Name:	us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration