Income Taxes (Significant components of the Company's deferred tax assets and liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax Assets:
Property and casualty claim and claim adjustment expense reserves	$ 178	$ 265
Unearned premium reserves	230	187
Receivables	29	35
Employee benefits	281	289
Life settlement contracts	48	46
Deferred retroactive reinsurance benefit	84	61
Investment valuation differences	29	0
Other assets	142	138
Gross deferred tax assets	1,021	1,021
Deferred Tax Liabilities:
Investment valuation differences	0	50
Deferred acquisition costs	117	226
Net unrealized gains	202	489
Other liabilities	64	65
Deferred Tax Liabilities, Gross	383	830
Net deferred tax asset (liability)	$ 638	$ 191