Derivatives - Credit Risk Related Contingent Features (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivative, Credit Risk Related Contingent Features
The aggregate fair value of all derivative instruments with credit-risk-related contingent features that were in a liability position	$ 15.0	$ 6.0
Required collateral assets to be posted if the credit-risk contingent features of these underlying agreements were triggered.	$ 14.0

The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

Name:	us-gaap_DerivativeNetLiabilityPositionAggregateFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant