Investments (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Investment income from portfolios
Investment income, net of expenses	$ 105	$ 108	$ 326	$ 326
Indemnity
Investment income from portfolios
Total investment income	5	4	13	13
Less: investment expenses	1	0	1	1
Investment income, net of expenses	4	4	12	12
Indemnity | Fixed maturities
Investment income from portfolios
Total investment income	4	3	10	10
Indemnity | Equity securities
Investment income from portfolios
Total investment income	0	1	2	2
Indemnity | Cash equivalents and other
Investment income from portfolios
Total investment income	1	0	1	1
Exchange
Investment income from portfolios
Total investment income	110	112	340	338
Less: investment expenses	9	8	26	24
Investment income, net of expenses	101	104	314	314
Exchange | Fixed maturities
Investment income from portfolios
Total investment income	87	91	266	275
Exchange | Equity securities
Investment income from portfolios
Total investment income	23	21	72	63
Exchange | Cash equivalents and other
Investment income from portfolios
Total investment income	$ 0	$ 0	$ 2	$ 0