Reinsurance (Reinsurance Recoverable by Category and Listing of Largest Reinsurers) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 15,906
Provision	$ 314	$ 316
% of Gross	2.00%
Largest reinsurers
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 7,267
Provision	$ 88
% of Gross	1.20%
Other reinsurers balances rated A- or better
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 4,901
Provision	$ 58
% of Gross	1.20%
Other reinsurers balances with ratings lower than A- or not rated
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 466
Provision	$ 64
% of Gross	13.70%
Other pools and government agencies
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 366
Provision	$ 14
% of Gross	3.80%
Structured settlements
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 521
Provision	$ 11
% of Gross	2.10%
Other captives
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 2,107
Provision	$ 11
% of Gross	0.50%
Other
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 278
Provision	$ 68
% of Gross	24.50%