Indemnity Accumulated Other Comprehensive Loss (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Change in other comprehensive loss, net of tax:
Unrealized appreciation of investments, net of tax	$ 224	$ 22	$ 118
Postretirement plans, net of tax	(30)	(41)	(4)
Change in other comprehensive loss, net of tax	150	(70)	91
Indemnity
Balance, beginning of period	(105)
Change in other comprehensive loss, net of tax:
Unrealized appreciation of investments, net of tax	2
Postretirement plans, net of tax	(30)
Change in other comprehensive loss, net of tax	(28)
Balance, end of period	(133)
Indemnity | Unrealized net appreciation of investments
Balance, beginning of period	11
Change in other comprehensive loss, net of tax:
Unrealized appreciation of investments, net of tax	2
Postretirement plans, net of tax
Change in other comprehensive loss, net of tax	2
Balance, end of period	13
Indemnity | Net losses associated with postretirement benefits
Balance, beginning of period	(116)
Change in other comprehensive loss, net of tax:
Unrealized appreciation of investments, net of tax
Postretirement plans, net of tax	(30)
Change in other comprehensive loss, net of tax	(30)
Balance, end of period	$ (146)