Income Taxes (Significant components of the Company's deferred tax assets and liabilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Deferred Tax Assets:
Property and casualty claim and claim adjustment expense reserves	$ 419	$ 525
Unearned premium reserves	142	127
Receivables	74	95
Employee benefits	323	258
Life settlement contracts	61	64
Investment valuation differences	3	70
Net loss and tax credits carried forward	25	84
Other assets	159	124
Gross deferred tax assets	1,206	1,347
Deferred Tax Liabilities:
Deferred acquisition costs	283	284
Net unrealized gains	508	314
Other liabilities	37	82
Gross deferred tax liabilities	828	680
Net deferred tax asset (liability)	$ 378	$ 667