Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Change in other comprehensive income (loss), net of tax:
Unrealized appreciation of investments, net of tax	$ 77	$ 8
Reclassification adjustment for gross gains included in income, net of tax	(5)	(12)
Change in other comprehensive income (loss), net of tax	72	(4)	(61)
Indemnity
Balance, beginning of period	(105)
Change in other comprehensive income (loss), net of tax:
Change in other comprehensive income (loss), net of tax	2		(52)
Balance, end of period	(103)		(105)
Indemnity | Unrealized net appreciation of investments
Balance, beginning of period	11
Change in other comprehensive income (loss), net of tax:
Unrealized appreciation of investments, net of tax	2
Reclassification adjustment for gross gains included in income, net of tax	0
Change in other comprehensive income (loss), net of tax	2
Balance, end of period	13
Indemnity | Net losses associated with postretirement benefits
Change in other comprehensive income (loss), net of tax:
Balance, end of period	(116)		(116)
Indemnity | Total
Balance, beginning of period	(105)
Change in other comprehensive income (loss), net of tax:
Unrealized appreciation of investments, net of tax	2
Reclassification adjustment for gross gains included in income, net of tax	0
Change in other comprehensive income (loss), net of tax	2
Balance, end of period	$ (103)