Statutory Requirements - Statutory EBS and BSCR (Details) - Bermuda - USD ($)	Dec. 31, 2020	Dec. 31, 2019
ALRe
Statutory Accounting Practices [Line Items]
EBS Capital and Surplus	$ 17,168,000,000	$ 14,073,000,000
BSCR ratio	254.00%	310.00%
Statutory Accounting Practices, Minimum Solvency Margin Required	$ 8,000,000
Statutory Accounting Practices, Minimum Solvency Margin, Percentage of Assets Threshold	2.00%
Statutory Accounting Practices, Minimum Solvency Margin, Assets Threshold	$ 500,000,000
Statutory Accounting Practices, Minimum Solvency Margin, Percentage of Assets In Excess of Threshold	1.50%
AARe
Statutory Accounting Practices [Line Items]
EBS Capital and Surplus	$ 2,441,000,000	$ 2,898,000,000
BSCR ratio	967.00%	257.00%
Statutory Accounting Practices, Minimum Solvency Margin Required	$ 8,000,000
Statutory Accounting Practices, Minimum Solvency Margin, Percentage of Assets Threshold	2.00%
Statutory Accounting Practices, Minimum Solvency Margin, Assets Threshold	$ 500,000,000
Statutory Accounting Practices, Minimum Solvency Margin, Percentage of Assets In Excess of Threshold	1.50%
ACRA
Statutory Accounting Practices [Line Items]
EBS Capital and Surplus	$ 2,945,000,000	$ 1,237,000,000
BSCR ratio	236.00%	341.00%
Statutory Accounting Practices, Minimum Solvency Margin, Assets Threshold	$ 500,000
Statutory Accounting Practices, Minimum Solvency Margin, Percentage of Assets In Excess of Threshold	1.50%