Related Parties (Details) - Pension Plans [Member] - Investment Management Services for Defined Benefit Plan [Member] - FS&C [Member] - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Related Party Transaction [Line Items]
Assets under Management, Carrying Amount	$ 158.4
Investment expenses	$ 0.5	$ 0.4

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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