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Investment Securities (Restrictions on Redemption Frequency and Advance Notice Requirements) (Details) $ in Millions	Sep. 30, 2017 USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Outstanding redemptions	$ 19.1
Semi-annual | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	73.8
Semi-annual | 30-59 days notice | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	54.7
Semi-annual | 60-89 days notice | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	$ 19.1
September 2018 | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of hedge funds	1
Other long-term investments	$ 54.7

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Amount of other investments classified as trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Trading Securities
-URI http://asc.fasb.org/extlink&oid=6526789

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26626-111562

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.(a),1(c),(d),(e),(f),(g))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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Outstanding redemptions that are subject to market fluctuations.

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