Employee Benefits - Narrative (Details) $ in Millions	6 Months Ended
Jun. 30, 2018 USD ($)
Retirement Benefits [Abstract]
Contribution towards retirement plans	$ 4
Expected contributions towards retirement plans, remainder of the year	$ 5

Amount of contribution received by defined benefit plan from employer which increases plan assets.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
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Name:	us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration