Investments (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Investment income from portfolios
Investment income, net of expenses	$ 104	$ 113	$ 207	$ 221
Indemnity
Investment income from portfolios
Total investment income	4	4	8	8
Less: investment expenses	1	0	1	0
Investment income, net of expenses	3	4	7	8
Indemnity | Fixed maturities
Investment income from portfolios
Total investment income	3	3	6	6
Indemnity | Equity securities
Investment income from portfolios
Total investment income	0	1	1	2
Indemnity | Cash equivalents and other
Investment income from portfolios
Total investment income	1	0	1	0
Exchange
Investment income from portfolios
Total investment income	110	117	217	230
Less: investment expenses	9	8	17	17
Investment income, net of expenses	101	109	200	213
Exchange | Fixed maturities
Investment income from portfolios
Total investment income	83	89	166	179
Exchange | Equity securities
Investment income from portfolios
Total investment income	27	27	51	49
Exchange | Cash equivalents and other
Investment income from portfolios
Total investment income	$ 0	$ 1	$ 0	$ 2