SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Stable Value Product Account Balances (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Summarized financial information for the company's segments
Stable value product account balances marketed through structured programs	$ 3,337.9	$ 1,872.5
Future maturities of stable value products
2018	888.0
2019 - 2020	2,479.5
2021 - 2022	1,201.0
Thereafter	$ 124.8
Minimum
Summarized financial information for the company's segments
Maturities of GICs and funding agreements	1 year
Maximum
Summarized financial information for the company's segments
Maturities of GICs and funding agreements	12 years

Represents the maturity period of the guaranteed investment contracts and funding agreements written by the entity.

No definition available.

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- Definition

Represents the liability as of the balance sheet date of amounts related to stable value contracts marketed through structured programs.

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No definition available.

+ Details

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- Definition

Represents the amount of stable value products maturing after year five following the date of the latest balance sheet.

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No definition available.

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- Definition

Represents the amount of stable value products maturing in year one following the date of the latest balance sheet.

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No definition available.

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- Definition

Represents the amount of stable value products maturing in years four and five following the date of the latest balance sheet.

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No definition available.

+ Details

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- Definition

Represents the amount of stable value products maturing in years two and three following the date of the latest balance sheet.

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No definition available.

+ Details

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Namespace Prefix:	pl_
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Period Type:	instant

- References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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