Property and Casualty Unpaid Losses and Loss Expenses (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Less: reinsurance recoverable	$ 166
Paid losses and loss expenses related to:
Add: reinsurance recoverable	168
Interest rate used to discount workers compensation loss reserves (as a percent)	2.50%
Property and casualty insurance operations
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Losses and loss expense reserves at January 1, – Gross	3,499	3,584	3,598
Less: reinsurance recoverable	151	188	200
Losses and loss expense reserves at January 1, – Net	3,348	3,396	3,398
Incurred losses and loss expenses related to:
Current accident year	3,494	3,616	3,053
Prior accident years	(115)	(272)	(244)
Total incurred losses and loss expenses	3,379	3,344	2,809
Paid losses and loss expenses related to:
Current accident year	2,166	2,360	1,855
Prior accident years	1,117	1,032	956
Total paid losses and loss expenses	3,283	3,392	2,811
Losses and loss expense reserves at December 31, – Net	3,444	3,348	3,396
Add: reinsurance recoverable	154	151	188
Losses and loss expense reserves at December 31, – Gross	3,598	3,499	3,584
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	85	84	127
Receivables for salvage and subrogation	$ 150	$ 145	$ 141