Stockholders' Equity and Statutory Accounting Practices Combined statutory capital and surplus and net income (loss) (Details) - Combined Continental Casualty Companies - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statutory Accounting Practices [Line Items]
Statutory Capital and Surplus	$ 10,708	$ 10,787
Statutory Net Income (Loss)	$ 800	$ 1,062	$ 1,405