FAIR VALUE MEASUREMENTS - MEASURED ON RECURRING BASIS (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 376.7		$ 582.5		$ 415.3	$ 436.0
Cash and cash equivalents held by variable interest entities	85.1		54.2
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	1,635.1		1,573.2
Loans Receivable, Fair Value Disclosure	267.5		272.0
Life Insurance, Corporate or Bank Owned, Amount	133.2		123.0
Hedge fund	17.4		16.1
Cash and Cash Equivalents, at Carrying Value	376.7		582.5
Cash and cash equivalents held by variable interest entities	85.1		54.2
Insurance liabilities for interest-sensitive products excluding embedded derivatives	11,936.1	[1]	12,153.7	[1]
Investment borrowings	1,850.2		1,650.8
Borrowings related to variable interest entities	1,035.1		767.0
Notes Payable, Fair Value Disclosure	868.6		1,004.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	0		0
Loans Receivable, Fair Value Disclosure	0		0
Life Insurance, Corporate or Bank Owned, Amount	0		0
Hedge fund	0		0
Cash and Cash Equivalents, at Carrying Value	255.5		432.3
Cash and cash equivalents held by variable interest entities	85.1		54.2
Insurance liabilities for interest-sensitive products excluding embedded derivatives	0	[1]	0	[1]
Investment borrowings	0		0
Borrowings related to variable interest entities	0		0
Notes Payable, Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	0		0
Loans Receivable, Fair Value Disclosure	0		0
Life Insurance, Corporate or Bank Owned, Amount	133.2		123.0
Hedge fund	17.4		16.1
Cash and Cash Equivalents, at Carrying Value	121.1		150.2
Cash and cash equivalents held by variable interest entities	0		0
Insurance liabilities for interest-sensitive products excluding embedded derivatives	0	[1]	0	[1]
Investment borrowings	1,899.0		1,702.0
Borrowings related to variable interest entities	1,019.9		752.2
Notes Payable, Fair Value Disclosure	886.5		1,100.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	1,685.9		1,682.1
Loans Receivable, Fair Value Disclosure	267.5		272.0
Life Insurance, Corporate or Bank Owned, Amount	0		0
Hedge fund	0		0
Cash and Cash Equivalents, at Carrying Value	0		0
Cash and cash equivalents held by variable interest entities	0		0
Insurance liabilities for interest-sensitive products excluding embedded derivatives	11,936.1	[1]	12,153.7	[1]
Investment borrowings	0		0
Borrowings related to variable interest entities	0		0
Notes Payable, Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	1,685.9		1,682.1
Loans Receivable, Fair Value Disclosure	267.5		272.0
Life Insurance, Corporate or Bank Owned, Amount	133.2		123.0
Hedge fund	17.4		16.1
Cash and Cash Equivalents, at Carrying Value	376.6		582.5
Cash and cash equivalents held by variable interest entities	85.1		54.2
Insurance liabilities for interest-sensitive products excluding embedded derivatives	11,936.1	[1]	12,153.7	[1]
Investment borrowings	1,899.0		1,702.0
Borrowings related to variable interest entities	1,019.9		752.2
Notes Payable, Fair Value Disclosure	$ 886.5		$ 1,100.3

[1] The estimated fair value of insurance liabilities for interest-sensitive products was approximately equal to its carrying value at September 30, 2013 and December 31, 2012. This was because interest rates credited on the vast majority of account balances approximate current rates paid on similar products and because these rates are not generally guaranteed beyond one year.