Investments Maturity profile (Details) (Trading securities [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Cost [Member]
Maturity Profile [Line Items]
One year or less	$ 312,599
More than one year through five years	5,042,314
More than five years through ten years	3,592,725
More than ten years	1,127,474
Subtotal	10,075,112
Mortgage/asset-backed securities	3,440,220
Total	13,515,332
Fair value [Member]
Maturity Profile [Line Items]
One year or less	313,261
More than one year through five years	5,168,357
More than five years through ten years	3,719,234
More than ten years	1,251,213
Subtotal	10,452,065
Mortgage/asset-backed securities	3,492,358
Total	$ 13,944,423

- Details

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- Definition

This item represents debt securities which are expected to mature after five years and through ten years of the balance sheet date and which are categorized as trading securities.

+ References

No definition available.

+ Details

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- Definition

This item represents debt securities which are expected to mature after one year and through five years of the balance sheet date and which are categorized as trading securities.

+ References

No definition available.

+ Details

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- Definition

This item represents debt securities which are expected to mature after ten years from the balance sheet date and which are categorized as trading securities.

+ References

No definition available.

+ Details

Name:	pre_TradingSecuritiesDebtMaturitiesAfterTenYears
Namespace Prefix:	pre_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents all debt maturities and short term investments by contractual maturity date.

+ References

No definition available.

+ Details

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- Definition

This item represents all debt maturities and short term investments with fixed contractual maturity dates.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

This item represents debt securities and short term investments which are expected to mature within one year of the balance sheet date and which are categorized as trading securities.

+ References

No definition available.

+ Details

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- Definition

This item represents debt securities, categorized as trading securities, which do not have a single maturity date and which the Company has decided to disclose separately.

+ References

No definition available.

+ Details

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