Postretirement Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Compensation and Retirement Disclosure [Abstract]
Postretirement benefit expenses reimbursed to Indemnity from the Exchange and EFL (as a percent)	58.00%
Cost of pension plans:
Service cost for benefits earned	$ 21	$ 17	$ 15
Interest cost on benefit obligation	24	23	21
Expected return on plan assets	(27)	(27)	(25)
Prior service cost amortization	1	1	1
Net actuarial loss amortization	11	6	3
Pension plan cost	$ 30	$ 20	$ 15