Organization Organization (Details) $ / shares in Units, $ in Millions							3 Months Ended		9 Months Ended
	Aug. 03, 2015 $ / shares	Jul. 20, 2015 $ / shares	Jul. 16, 2015 $ / shares	Jul. 07, 2015 $ / shares	May. 03, 2015 USD ($) $ / shares	Jan. 25, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 shares	Sep. 30, 2015 USD ($)	May. 12, 2015 $ / shares	Apr. 14, 2015 $ / shares
PartnerRe Ltd. [Member]
Business Acquisition [Line Items]
Share Exchange Ratio Upon Amalgamation | shares								2.18
Special Dividend Per Share			$ 17.50		$ 11.50
Axis Capital Holdings Ltd [Member]
Business Acquisition [Line Items]
Share Exchange Ratio Upon Amalgamation | shares								1.00
Termination Fee | $					$ 280	$ 250
Termination Fee Paid | $							$ 315		$ 315
EXOR S.p.A. [Member]
Business Acquisition [Line Items]
Special Dividend Per Share	$ 3.00	$ 3.00
Termination Fee | $									$ 250
Business Acquisition, Share Price	$ 137.50									$ 137.50	$ 130.00
Preferred stock interest rate change				100
Maximum earnings distributable				67.00%
Business acquisition percentage of voting interests proposed to be acquired											100.00%