Reinsurance (Reinsurance on premiums - short-duration contracts) (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2015
Premiums Earned, Net, by Business [Abstract]
Total net earned premiums	$ 1,385,000,000	$ 1,282,000,000	$ 1,223,000,000
Property and casualty [Member]
Premiums Earned, Net, by Business [Abstract]
Number of types of reinsurance agreements	3
Maximum recovery per loss by entity	5,000,000
Maximum amount of life insurance risk retained by the entity on a single life	750,000
Catastrophe reinsurance loss recovery per event by entity	125,000,000			155,000,000
Maximum amount of auto and home catastrophe insurance risk retained by entity per event	20,000,000			20,000,000
Percentage of personal umbrella, loss ceded	80.00%
Maximum personal umbrella, recovery	5,000,000
Short duration contracts [Member]
Premiums Written, Net [Abstract]
Direct premiums written	1,025,000,000	900,000,000	814,000,000
Ceded premiums written	(17,000,000)	(16,000,000)	(13,000,000)
Total net written premiums	1,008,000,000	884,000,000	801,000,000
Premiums Earned, Net, by Business [Abstract]
Direct premiums earned	979,000,000	868,000,000	795,000,000
Ceded premiums earned	(17,000,000)	(16,000,000)	(14,000,000)
Total net earned premiums	$ 962,000,000	$ 852,000,000	$ 781,000,000