Dividends (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended												12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 08, 2018
Dividends Paid [Line Items]
Dividends per share paid on ordinary shares														$ 0.88	$ 0.80	$ 0.72
Ordinary shares
Dividends Paid [Line Items]
Dividends per share paid on ordinary shares		$ 0.22	$ 0.22	$ 0.22	$ 0.22	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.16	$ 0.16
Series D preference ordinary shares
Dividends Paid [Line Items]
Dividends on preference ordinary shares	[1]													$ 13.9	$ 12.9	$ 11.8
Series E preference ordinary shares
Dividends Paid [Line Items]
Dividends on preference ordinary shares	[2]													45.2	65.0	65.1
Subsequent Event [Member] | Series D preference ordinary shares
Dividends Paid [Line Items]
Dividends declared and payable per share																	$ 11.4468
Subsequent Event [Member] | Series E preference ordinary shares
Dividends Paid [Line Items]
Dividends declared and payable per share																	9.7537
Catlin Group Limited [Member] | Noncumulative perpetual preferred shares
Dividends Paid [Line Items]
Dividends on preference ordinary shares	[3]													$ 39.6	$ 43.5	$ 21.8
Catlin Group Limited [Member] | Subsequent Event [Member] | Noncumulative perpetual preferred shares
Dividends Paid [Line Items]
Dividends declared and payable per share																	$ 6,100,000

[1] On January 8, 2018, the Board of Directors of XLIT resolved to pay a dividend of $11.4468 per share on XLIT's Series D Preference Ordinary Shares. The dividend was paid on January 16, 2018 to all shareholders of record at January 8, 2018.

[2] On January 8, 2018, the Board of Directors of XLIT resolved on January 8, 2018 to pay a dividend of $9.7537 per share on XLIT's Series E Preference Ordinary Shares. The dividend was paid on January 16, 2018 to all shareholders of record at January 8, 2018.

[3] On January 8, 2018, the Board of Directors of Catlin-Bermuda resolved to pay a dividend in the aggregate amount of $6.1 million on CICL Prefs. The dividend was paid on January 19, 2018 to all shareholders of record at December 31, 2017.