Statutory Information - Summary of statutory capital, surplus and net income (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Bermuda
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	[1]	$ 13,511,729	$ 11,605,652
Required statutory capital and surplus	[1]	5,492,968	4,718,345
Statutory net income (loss)		1,876,416	919,554	$ 881,665
Ireland
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	[1]	721,439	653,055
Required statutory capital and surplus	[1]	542,703	429,117
Statutory net income (loss)		26,367	29,223	(14,438)
United States
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	[1]	4,440,848	4,195,477
Required statutory capital and surplus	[1]	1,697,640	1,783,268
Statutory net income (loss)		481,188	292,831	500,412
United Kingdom
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	[1]	748,276	386,892
Required statutory capital and surplus	[1]	349,328	271,864
Statutory net income (loss)		(17,423)	(18,467)	(33,257)
Canada
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	[1]	61,351	59,096
Required statutory capital and surplus	[1]	32,763	33,189
Statutory net income (loss)		$ (1,023)	$ 2,525	$ 158

[1] Such amounts include ownership interests in affiliated insurance and reinsurance subsidiaries.