Earnings Per Share (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Class A | Indemnity
Income available to stockholders
Allocated net income (numerator) (in dollars)									$ 168	$ 161	$ 107
Weighted shares (denominator)									48,875,316	50,705,607	51,250,606
Per-share amount (in dollars per share)	$ 0.55	$ 0.97	$ 1.05	$ 0.88	$ 0.25	$ 1.05	$ 0.96	$ 0.92	$ 3.45	$ 3.18	$ 2.10
Dilutive effect of stock awards
Allocated net income (numerator) (in dollars)									0	0	0
Weighted shares (denominator) (in shares)									71,721	68,887	60,793
Assumed conversion of Class B shares
Allocated net income (numerator) (in dollars)									1	1	1
Weighted shares (denominator)									6,110,400	6,110,400	6,117,600
Income available to stockholders on equivalent shares
Allocated net income (numerator) (in dollars)									169	162	108
Weighted shares (denominator) (in shares)									55,057,437	56,884,894	57,428,999
Per-share amount (in dollars per share)	$ 0.49	$ 0.87	$ 0.94	$ 0.78	$ 0.22	$ 0.94	$ 0.86	$ 0.82	$ 3.08	$ 2.85	$ 1.89
Class B
Indemnity Earnings Per Share Calculation
Ratio for converting shares of Class B common stock into shares of Class A common stock, numerator (in Class A shares)	2,400								2,400
Ratio for converting shares of Class B common stock into shares of Class A common stock, denominator (in Class B shares)	1								1
Class B | Indemnity
Indemnity Earnings Per Share Calculation
Ratio for converting shares of Class B common stock into shares of Class A common stock, numerator (in Class A shares)	2,400				2,400				2,400	2,400
Ratio for converting shares of Class B common stock into shares of Class A common stock, denominator (in Class B shares)	1				1				1	1
Income available to stockholders
Allocated net income (numerator) (in dollars)									1	1	1
Weighted shares (denominator)									2,546	2,546	2,549
Per-share amount (in dollars per share)	$ 81.76	$ 146.67	$ 158.33	$ 126.48	$ 40.93	$ 150.87	$ 138.21	$ 132.83	$ 522.47	$ 462.83	$ 312.45
Income available to stockholders on equivalent shares
Allocated net income (numerator) (in dollars)									$ 1	$ 1	$ 1
Weighted shares (denominator) (in shares)									2,546	2,546	2,549
Per-share amount (in dollars per share)	$ 81.76	$ 146.67	$ 158.33	$ 126.48	$ 40.93	$ 150.87	$ 138.21	$ 132.83	$ 522.47	$ 462.83	$ 312.45