Debt and Credit Facilities Credit Facilities (Details) - Eight Hundred Million Credit Facility Expiring November 2018 [Member]	Apr. 30, 2017 USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 800,000,000
Line of Credit Facility, Covenant Compliance, Ratio of Earnings Before Interest, Taxes, Deprecation, and Amortization to Consolidated Interest Expense	3

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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