NOTES PAYABLE - DIRECT CORPORATE OBLIGATIONS - SCHEDULE OF LONG-TERM DEBT INSTRUMENTS (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Debt Instruments [Abstract]
Direct corporate obligations	$ 913.4	$ 912.9
Unamortized debt issue costs	(11.6)	(12.1)
Senior notes [Member] \| 4.500% Senior Notes due May 2020 [Member]
Debt Instruments [Abstract]
Direct corporate obligations	$ 325.0	325.0
Interest rate	4.50%
Senior notes [Member] \| 5.250% Senior Notes due May 2025 [Member]
Debt Instruments [Abstract]
Direct corporate obligations	$ 500.0	500.0
Interest rate	5.25%
Line of credit [Member] \| Revolving Credit Agreement [Member]
Debt Instruments [Abstract]
Direct corporate obligations	$ 100.0	$ 100.0

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: 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(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: 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(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, before accumulated amortization, of debt issuance costs classified as noncurrent. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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