Variable Interest Entities and Noncontrolling Interests - Variable interest entity (Details) (Variable Interest Entity, Primary Beneficiary, Watford Holdings Ltd, USD $)	1 Months Ended
	Mar. 31, 2014
Variable Interest Entity, Primary Beneficiary | Watford Holdings Ltd
Variable Interest Entity [Line Items]
Initial capitalization amount	$ 1,100,000,000
Proceeds from issuance of common shares	907,300,000
Net proceeds from issuance of common shares	895,600,000
Proceeds on issuance of preference shares	226,600,000
Net proceeds on issuance of preference shares	219,200,000
Initial investment contribution amount	$ 100,000,000
Ownership percentage	11.00%