Property and Casualty Unpaid Losses and Loss Expenses (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of property and casualty beginning and ending loss and loss expense reserve balances
Less: reinsurance recoverable, beginning of year	$ 172
Incurred losses and loss expenses related to:
Current accident year	3,969	3,379	3,494
Prior accident years	(116)	(19)	(115)
Paid losses and loss expenses related to:
Add: reinsurance recoverable, end of year	161	172
Property and Casualty Group
Reconciliation of property and casualty beginning and ending loss and loss expense reserve balances
Losses and loss expense reserves, beginning of year – Gross	3,747	3,598	3,499
Less: reinsurance recoverable, beginning of year	156	154	151
Losses and loss expense reserves, beginning of year – Net	3,591	3,444	3,348
Incurred losses and loss expenses related to:
Current accident year	3,969	3,379	3,494
Prior accident years	(116)	(19)	(115)
Total incurred losses and loss expenses	3,853	3,360	3,379
Paid losses and loss expenses related to:
Current accident year	2,513	2,007	2,166
Prior accident years	1,220	1,206	1,117
Total paid losses and loss expenses	3,733	3,213	3,283
Losses and loss expense reserves, end of year – Net	3,711	3,591	3,444
Add: reinsurance recoverable, end of year	142	156	154
Losses and loss expense reserves, end of year – Gross	3,853	3,747	3,598
Workers' compensation discount
Interest rate used to discount workers compensation loss reserves (as a percent)	2.50%	2.50%	2.50%
Reduction in unpaid losses and loss expenses as a result of discounting workers compensation loss reserves	89	85	85
Salvage and subrogation
Receivables for salvage and subrogation	$ 171	$ 149	$ 150