Investments (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Investment income from portfolios
Investment income, net of expenses	$ 108	$ 105
Indemnity
Investment income from portfolios
Total investment income	4	4
Less: Investment expenses	0	0
Investment income, net of expenses	4	4
Indemnity | Fixed maturities
Investment income from portfolios
Total investment income	3	3
Indemnity | Equity securities
Investment income from portfolios
Total investment income	1	1
Indemnity | Cash equivalents and other
Investment income from portfolios
Total investment income	0	0
Exchange
Investment income from portfolios
Total investment income	113	110
Less: Investment expenses	9	9
Investment income, net of expenses	104	101
Exchange | Fixed maturities
Investment income from portfolios
Total investment income	90	92
Exchange | Equity securities
Investment income from portfolios
Total investment income	22	18
Exchange | Cash equivalents and other
Investment income from portfolios
Total investment income	$ 1	$ 0