FAIR VALUE MEASUREMENTS - MEASUREMENTS BY INPUT LEVEL (Details) - USD ($) $ in Millions | Jun. 30, 2015 | Dec. 31, 2014 |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | $ 20,224.8 | $ 20,634.9 |
Trading securities | 257.5 | 244.9 |
Investments held by variable interest entities - corporate securities | 1,565.6 | 1,367.1 |
Assets held in separate accounts | 5.4 | 5.6 |
Level 1 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Trading securities | 3.4 | 3.5 |
Investments held by variable interest entities - corporate securities | 0 | 0 |
Assets held in separate accounts | 0 | 0 |
Total assets carried at fair value by category | 234.6 | 221.8 |
Level 2 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Trading securities | 214.2 | 212.8 |
Investments held by variable interest entities - corporate securities | 1,565.6 | 1,367.1 |
Assets held in separate accounts | 5.4 | 5.6 |
Total assets carried at fair value by category | 22,058.6 | 22,039.5 |
Level 3 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Trading securities | 39.9 | 28.6 |
Investments held by variable interest entities - corporate securities | 0 | 0 |
Assets held in separate accounts | 0 | 0 |
Total assets carried at fair value by category | 258.2 | 518.8 |
Corporate debt securities [Member] | Level 1 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 0 |
Equity securities - corporate securities | 230.2 | 216.9 |
Trading securities | 0 | 0 |
Corporate debt securities [Member] | Level 2 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 13,383.2 | 13,605.1 |
Equity securities - corporate securities | 173.2 | 174.1 |
Trading securities | 24.9 | 24.3 |
Corporate debt securities [Member] | Level 3 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 133.7 | 365.9 |
Equity securities - corporate securities | 29.9 | 28 |
Trading securities | 0 | 0 |
US treasury and government [Member] | Level 1 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 0 |
Trading securities | 0 | 0 |
US treasury and government [Member] | Level 2 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 166.2 | 168.9 |
Trading securities | 3.1 | 3.7 |
US treasury and government [Member] | Level 3 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 0 |
Trading securities | 0 | 0 |
US states and political subdivisions debt securities [Member] | Level 1 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 0 |
US states and political subdivisions debt securities [Member] | Level 2 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 2,201.4 | 2,242.2 |
US states and political subdivisions debt securities [Member] | Level 3 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 35.5 |
Foreign government debt securities [Member] | Level 1 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 0 |
Foreign government debt securities [Member] | Level 2 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 1.9 | 1.9 |
Foreign government debt securities [Member] | Level 3 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 0 |
Asset-backed securities [Member] | Level 1 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 0 |
Trading securities | 0 | 0 |
Asset-backed securities [Member] | Level 2 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 1,352.7 | 1,209.8 |
Trading securities | 21.4 | 24 |
Asset-backed securities [Member] | Level 3 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 53.3 | 59.2 |
Trading securities | 0 | 0 |
Collateralized debt obligations [Member] | Level 1 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 0 |
Collateralized debt obligations [Member] | Level 2 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 344.3 | 324.5 |
Collateralized debt obligations [Member] | Level 3 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 0 |
Commercial mortgage backed securities [Member] | Level 1 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 0 |
Trading securities | 0 | 0 |
Commercial mortgage backed securities [Member] | Level 2 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 1,381.4 | 1,275.1 |
Trading securities | 137.8 | 131 |
Commercial mortgage backed securities [Member] | Level 3 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 1.2 | 1.2 |
Trading securities | 39.9 | 28.6 |
Mortgage pass through securities [Member] | Level 1 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 0 |
Trading securities | 0 | 0 |
Mortgage pass through securities [Member] | Level 2 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 3.6 | 4.2 |
Trading securities | 0.1 | 0.1 |
Mortgage pass through securities [Member] | Level 3 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0.2 | 0.4 |
Trading securities | 0 | 0 |
Collateralized mortgage obligations [Member] | Level 1 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 0 |
Trading securities | 0 | 0 |
Collateralized mortgage obligations [Member] | Level 2 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 1,201.7 | 1,341 |
Trading securities | 26.9 | 29.7 |
Collateralized mortgage obligations [Member] | Level 3 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 0 |
Trading securities | 0 | 0 |
Total fixed maturities, available for sale [Member] | Level 1 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 0 | 0 |
Total fixed maturities, available for sale [Member] | Level 2 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 20,036.4 | 20,172.7 |
Total fixed maturities, available for sale [Member] | Level 3 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 188.4 | 462.2 |
Equity securities [Member] | Level 1 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Trading securities | 3.4 | 3.5 |
Equity securities [Member] | Level 2 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Trading securities | 0 | 0 |
Equity securities [Member] | Level 3 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Trading securities | 0 | 0 |
Derivatives [Member] | Level 1 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Other invested assets - derivatives | 1 | 1.4 |
Derivatives [Member] | Level 2 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Other invested assets - derivatives | 63.8 | 107.2 |
Derivatives [Member] | Level 3 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Other invested assets - derivatives | 0 | 0 |
Embedded derivatives associated with fixed index annuity products [Member] | Level 1 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Future policy benefits - embedded derivatives associated with fixed index annuity products | 0 | 0 |
Embedded derivatives associated with fixed index annuity products [Member] | Level 2 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Future policy benefits - embedded derivatives associated with fixed index annuity products | 0 | 0 |
Embedded derivatives associated with fixed index annuity products [Member] | Level 3 [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Future policy benefits - embedded derivatives associated with fixed index annuity products | 1,074 | 1,081.5 |
Estimate of fair value measurement [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Trading securities | 257.5 | 244.9 |
Investments held by variable interest entities - corporate securities | 1,565.6 | 1,367.1 |
Assets held in separate accounts | 5.4 | 5.6 |
Total assets carried at fair value by category | 22,551.4 | 22,780.1 |
Estimate of fair value measurement [Member] | Corporate debt securities [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 13,516.9 | 13,971 |
Equity securities - corporate securities | 433.3 | 419 |
Trading securities | 24.9 | 24.3 |
Estimate of fair value measurement [Member] | US treasury and government [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 166.2 | 168.9 |
Trading securities | 3.1 | 3.7 |
Estimate of fair value measurement [Member] | US states and political subdivisions debt securities [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 2,201.4 | 2,277.7 |
Estimate of fair value measurement [Member] | Foreign government debt securities [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 1.9 | 1.9 |
Estimate of fair value measurement [Member] | Asset-backed securities [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 1,406 | 1,269 |
Trading securities | 21.4 | 24 |
Estimate of fair value measurement [Member] | Collateralized debt obligations [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 344.3 | 324.5 |
Estimate of fair value measurement [Member] | Commercial mortgage backed securities [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 1,382.6 | 1,276.3 |
Trading securities | 177.7 | 159.6 |
Estimate of fair value measurement [Member] | Mortgage pass through securities [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 3.8 | 4.6 |
Trading securities | 0.1 | 0.1 |
Estimate of fair value measurement [Member] | Collateralized mortgage obligations [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 1,201.7 | 1,341 |
Trading securities | 26.9 | 29.7 |
Estimate of fair value measurement [Member] | Total fixed maturities, available for sale [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total fixed maturities, available for sale | 20,224.8 | 20,634.9 |
Estimate of fair value measurement [Member] | Equity securities [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Trading securities | 3.4 | 3.5 |
Estimate of fair value measurement [Member] | Derivatives [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Other invested assets - derivatives | 64.8 | 108.6 |
Estimate of fair value measurement [Member] | Embedded derivatives associated with fixed index annuity products [Member] | Fair value, measurements, recurring [Member] | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Future policy benefits - embedded derivatives associated with fixed index annuity products | $ 1,074 | $ 1,081.5 |