Receivables From Customers, Net and Notes Receivable, Net Receivables from Customers, Net and Notes Receivables, Net - Bad Debt Expense and Recoveries (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)		$ 1.3
Provision for Doubtful Accounts		2.6
Commercial Hedging [Member]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)		1.1	$ 2.7
Provision for Doubtful Accounts	$ 1.3		3.8
Securities [Member]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)		$ 0.2	$ 0.3

Amount of expense related to write-down of receivables to the amount expected to be collected. Includes, but is not limited to, accounts receivable and notes receivable.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.5)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

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