Investments (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Investment income from portfolios
Investment income, net of expenses	$ 103	$ 108
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	107	113
Less: investment expenses	8	9
Investment income, net of expenses	99	104
Exchange | Fixed maturities
Investment income from portfolios
Total investment income	83	90
Exchange | Equity securities
Investment income from portfolios
Total investment income	24	22
Exchange | Cash equivalents and other
Investment income from portfolios
Total investment income	$ 0	$ 1