Derivative Instruments and Hedging Activities - Impact of Derivative Instruments on Consolidated Statements of Income and Accumulated OCI (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest Expense and Other
Derivative Instruments, Gain (Loss) [Line Items]
Loss Reclassified from Accumulated OCI into Income (Effective Portion)	$ (5.3)	$ (5.7)	$ (5.7)
Treasury Locks, Net Of Tax
Derivative Instruments, Gain (Loss) [Line Items]
Net Loss Recognized in Accumulated OCI (Effective Portion)	$ (10.2)	$ (14.2)

The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4D
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624177-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration