Insurance (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reinsurance
Direct premiums written	$ 4,283	$ 4,061	$ 3,542
Reinsurance assumed	38	45	47
Reinsurance ceded	(1,372)	(1,336)	(1,181)
Net written premiums	2,949	2,770	2,408
Direct premiums earned	4,120	4,062	3,653
Reinsurance assumed	36	41	45
Reinsurance ceded	(1,309)	(1,344)	(1,148)
Net earned premiums	2,847	2,759	2,550
Reinsurance recoveries	$ 1,743	$ 770	$ 395