Statutory Requirements Statutory Permitted Practices (Details) - Bermuda $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
ALRe
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Permitted Practice, Increase (Decrease) To Capital And Surplus	$ 554
Statutory Accounting Practices, Permitted Practice, Increase (Decrease) To Statutory Net Income	(705)
AARe
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Permitted Practice, Increase (Decrease) To Capital And Surplus	202
Statutory Accounting Practices, Permitted Practice, Increase (Decrease) To Statutory Net Income	179
ACRA
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Permitted Practice, Increase (Decrease) To Capital And Surplus	(252)
Statutory Accounting Practices, Permitted Practice, Increase (Decrease) To Statutory Net Income	$ (267)