CONSOLIDATED STATEMENTS OF FINANCIAL POSITION (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Cash and cash equivalents	$ 388	$ 400
Other assets	414	456
Indemnity
Fixed maturities, amortized cost	406	437
Equity securities, cost	47	54
Trading securities, cost
Limited partnerships, cost	142	151
Cash and cash equivalents	41	12
Other assets	115	117
Treasury stock (in shares)	21,596,082	21,406,519
Exchange
Fixed maturities, amortized cost	7,242	7,016
Equity securities, cost	857	871
Trading securities, cost	2,011	1,910
Limited partnerships, cost	880	913
Cash and cash equivalents	347	388
Other assets	$ 299	$ 339
Class A | Indemnity
Common stock, stated value per share (in dollars per share)	$ 0.0292	$ 0.0292
Common stock, authorized (in shares)	74,996,930	74,996,930
Common stock, issued (in shares)	68,299,200	68,299,200
Common stock, outstanding (in shares)	46,703,118	46,892,681
Class B | Indemnity
Ratio for converting shares of Class B common stock into shares of Class A common stock (as a percent)	2400.00%	2400.00%
Common stock, stated value per share (in dollars per share)	$ 70	$ 70
Common stock, authorized (in shares)	3,070	3,070
Common stock, issued (in shares)	2,542	2,542
Common stock, outstanding (in shares)	2,542	2,542