Retirement Benefits - Summary of Components of Retirement Benefit Expense (Income) (Footnote) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2015
Retirement Benefits [Abstract]
Actual gain (loss) on assets	$ (22.2)	$ 96.8	$ 93.7	$ (64.2)
Actual rate of return on assets	(2.30%)	10.80%	11.00%	(6.10%)

Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration