Investments (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Investment income from portfolios
Investment income, net of expenses	$ 113	$ 113	$ 221	$ 218
Indemnity
Investment income from portfolios
Total investment income	4	5	8	9
Less: investment expenses	0	1	0	1
Investment income, net of expenses	4	4	8	8
Indemnity | Fixed maturities
Investment income from portfolios
Total investment income	3	4	6	7
Indemnity | Equity securities
Investment income from portfolios
Total investment income	1	0	2	1
Indemnity | Cash equivalents and other
Investment income from portfolios
Total investment income	0	1	0	1
Exchange
Investment income from portfolios
Total investment income	117	116	230	226
Less: investment expenses	8	7	17	16
Investment income, net of expenses	109	109	213	210
Exchange | Fixed maturities
Investment income from portfolios
Total investment income	89	92	179	184
Exchange | Equity securities
Investment income from portfolios
Total investment income	27	24	49	42
Exchange | Cash equivalents and other
Investment income from portfolios
Total investment income	$ 1	$ 0	$ 2	$ 0