Reinsurance (Reinsurance Recoverable by Category and Listing of Largest Reinsurers) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross reinsurance recoverable	$ 11,714
Provision	$ 328	$ 357
% of Gross	2.80%
Largest reinsurers
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross reinsurance recoverable	$ 5,335
Provision	$ 69
% of Gross	1.30%
Other reinsurers balances rated A- or better
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross reinsurance recoverable	$ 3,078
Provision	$ 44
% of Gross	1.40%
Other reinsurers balances with ratings lower than A- or not rated
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross reinsurance recoverable	$ 378
Provision	$ 68
% of Gross	18.00%
Other pools and government agencies
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross reinsurance recoverable	$ 347
Provision	$ 14
% of Gross	4.00%
Structured settlements
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross reinsurance recoverable	$ 546
Provision	$ 10
% of Gross	1.80%
Other captives
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross reinsurance recoverable	$ 1,786
Provision	$ 23
% of Gross	1.30%
Other
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross reinsurance recoverable	$ 244
Provision	$ 100
% of Gross	41.00%