Benefit Plans - Expected Contributions to Pension and Other Postretirement Benefit Plans (Details) $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($)
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Expected contributions in 2016	$ 0.0
SERP and Directors' Plan
Defined Benefit Plan Disclosure [Line Items]
Expected contributions in 2016	6.8
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected contributions in 2016	$ 1.1

Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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