Reinsurance (Reinsurance Recoverable by Category and Listing of Largest Reinsurers) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 15,497
Provision	$ 316	$ 323
% of Gross	2.00%
Largest reinsurers
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 6,594
Provision	$ 72
% of Gross	1.10%
Other reinsurers balances rated A- or better
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 4,624
Provision	$ 55
% of Gross	1.20%
Other reinsurers balances with ratings lower than A- or not rated
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 478
Provision	$ 70
% of Gross	14.60%
Other pools and government agencies
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 379
Provision	$ 15
% of Gross	4.00%
Structured settlements
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 535
Provision	$ 15
% of Gross	2.80%
Other captives
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 2,647
Provision	$ 20
% of Gross	0.80%
Other
Ceded Credit Risk [Line Items]
Gross reinsurance recoverable	$ 240
Provision	$ 69
% of Gross	28.80%