Insurance (Details 2) (Property and casualty insurance [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property and casualty insurance [Member]
Effects of Reinsurance [Line Items]
Direct premiums written	$ 5,387	$ 4,744	$ 4,283
Reinsurance assumed	90	61	38
Reinsurance ceded	(1,457)	(1,464)	(1,372)
Net written premiums	4,020	3,341	2,949
Direct premiums earned	5,195	4,684	4,120
Reinsurance assumed	75	45	36
Reinsurance ceded	(1,392)	(1,525)	(1,309)
Net earned premiums	3,878	3,204	2,847
Reinsurance recoveries	$ 895	$ 1,255	$ 1,743