Computation of Earnings Per Ordinary Share and Ordinary Share Equivalent - Computation of Basic and Diluted Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Basic earnings per ordinary share & ordinary share equivalents outstanding:
Net income (loss) attributable to ordinary shareholders	$ 36,281us-gaap_NetIncomeLoss	$ 255,717us-gaap_NetIncomeLoss
Weighted average ordinary shares outstanding - basic	255,724	276,337
Basic earnings per ordinary share & ordinary share equivalents outstanding	$ 0.14us-gaap_EarningsPerShareBasic	$ 0.93us-gaap_EarningsPerShareBasic
Diluted earnings per ordinary share & ordinary share equivalents outstanding:
Impact of share-based compensation and certain conversion features	4,980	4,121
Weighted average ordinary shares outstanding - diluted	260,704	280,458
Diluted earnings per ordinary share & ordinary share equivalents outstanding	$ 0.14us-gaap_EarningsPerShareDiluted	$ 0.91us-gaap_EarningsPerShareDiluted
Dividends per ordinary share	$ 0.16	$ 0.16

Computation of Earnings Per Ordinary Share and Ordinary Share Equivalent - Computation of Basic and Diluted Earnings Per Share (Details) (USD $)
In Thousands, except Per Share data, unless otherwise specified

3 Months Ended

Mar. 31, 2015

Mar. 31, 2014

Basic earnings per ordinary share & ordinary share equivalents outstanding:

Net income (loss) attributable to ordinary shareholders

$ 36,281us-gaap_NetIncomeLoss

$ 255,717us-gaap_NetIncomeLoss

Weighted average ordinary shares outstanding - basic

255,724us-gaap_WeightedAverageNumberOfSharesOutstandingBasic

276,337us-gaap_WeightedAverageNumberOfSharesOutstandingBasic

Basic earnings per ordinary share & ordinary share equivalents outstanding

$ 0.14us-gaap_EarningsPerShareBasic

$ 0.93us-gaap_EarningsPerShareBasic

Diluted earnings per ordinary share & ordinary share equivalents outstanding:

Impact of share-based compensation and certain conversion features

4,980xlgroup_ImpactOfAssumedConversionOfUnits

4,121xlgroup_ImpactOfAssumedConversionOfUnits

Weighted average ordinary shares outstanding - diluted

260,704us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding

280,458us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding

Diluted earnings per ordinary share & ordinary share equivalents outstanding

$ 0.14us-gaap_EarningsPerShareDiluted

$ 0.91us-gaap_EarningsPerShareDiluted

Dividends per ordinary share

$ 0.16us-gaap_CommonStockDividendsPerShareCashPaid

- Definition

Aggregate dividends paid during the period for each share of common stock outstanding.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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