Dividends (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended												12 Months Ended
		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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Feb. 16, 2017	Jan. 12, 2017	Dec. 29, 2016	Oct. 28, 2016
Dividends Paid [Line Items]
Dividends per share paid on ordinary shares														$ 0.80	$ 0.72	$ 0.64
Ordinary shares
Dividends Paid [Line Items]
Dividends per share paid on ordinary shares		$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16
Series D preference ordinary shares
Dividends Paid [Line Items]
Dividends on preference ordinary shares	[1],[2]													$ 12.9	$ 11.8	$ 11.7
Dividends declared and payable per share																			$ 0.3525	$ 10.2222
Series E preference ordinary shares
Dividends Paid [Line Items]
Dividends on preference ordinary shares	[3]													65.0	65.1	65.1
Subsequent Event [Member] | Series D preference ordinary shares
Dividends Paid [Line Items]
Dividends declared and payable per share																	$ 10.473
Subsequent Event [Member] | Series E preference ordinary shares
Dividends Paid [Line Items]
Dividends declared and payable per share																	$ 32.50
Catlin Group Limited [Member] | Noncumulative perpetual preferred shares
Dividends Paid [Line Items]
Dividends on preference ordinary shares	[4]													$ 43.5	$ 21.8	$ 0.0
Catlin Group Limited [Member] | Subsequent Event [Member] | Noncumulative perpetual preferred shares
Dividends Paid [Line Items]
Dividends declared and payable per share																		$ 21,800,000

[1] On February 17, 2017, the Company announced that the Board of Directors of XL-Cayman resolved on February 16, 2017 to pay a dividend of $10.473 per share on XL-Cayman’s Series D Preference Ordinary Shares. The dividend will be paid on April 18, 2017 to all shareholders of record at April 14, 2017.

[2] On October 28, 2016, the Company announced that the Board of Directors of XL-Cayman resolved to pay a dividend of $10.2222 per share on XL-Cayman’s Series D Preference Ordinary Shares. The dividend was paid on January 17, 2017 to all shareholders of record at January 13, 2017. On December 29, 2016, the Board of Directors of XL-Cayman also resolved to pay an additional one-time dividend of $0.3525 per share on XL-Cayman's Series D Preference Ordinary Shares. The dividend was paid on January 17, 2017 to all shareholders of record at January 13, 2017.

[3] On February 17, 2017, the Company announced that the Board of Directors of XL-Cayman resolved on February 16, 2017 to pay a dividend of $32.50 per share on XL-Cayman’s Series E Preference Ordinary Shares. The dividend will be paid on April 18, 2017 to all shareholders of record at April 14, 2017.

[4] On January 12, 2017, the Board of Directors of Catlin-Bermuda resolved to pay a dividend in the aggregate amount of $21.8 million on CICL Prefs. The dividend was paid on January 19, 2017 to all shareholders of record at December 31, 2016.