Property and Casualty Unpaid Losses and Loss Expenses (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Property and casualty unpaid losses and loss expenses
Less: reinsurance recoverable	$ 201
Paid losses and loss expenses related to:
Add: reinsurance recoverable	166
Interest rate used to discount workers compensation loss reserves (as a percent)	2.50%
Property and casualty insurance operations
Property and casualty unpaid losses and loss expenses
Losses and loss expense reserves at beginning of period - Gross	3,584	3,598	3,586
Less: reinsurance recoverable	188	200	187
Losses and loss expense reserves at beginning of period - Net	3,396	3,398	3,399
Incurred losses and loss expenses related to:
Current accident year	3,616	3,053	2,732
Prior accident years	(272)	(244)	(93)
Total incurred losses and loss expenses	3,344	2,809	2,639
Paid losses and loss expenses related to:
Current accident year	2,360	1,855	1,608
Prior accident years	1,032	956	1,032
Total paid losses and loss expenses	3,392	2,811	2,640
Losses and loss expense reserves at end of period - Net	3,348	3,396	3,398
Add: reinsurance recoverable	151	188	200
Losses and loss expense reserves at end of period - Gross	3,499	3,584	3,598
Interest rate used to discount workers compensation loss reserves (as a percent)	2.50%
Reduction in unpaid losses and loss expenses as a result of discounting workers compensation loss reserves	84	127	136
Receivables for salvage and subrogation	$ 145	$ 141	$ 133