Shareholders' Equity and Noncontrolling Interest (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Reconciliation of the beginning and ending balances of shareholders' equity and noncontrolling interest
Balance, beginning of period	$ 6,293	$ 6,334	$ 6,334
Net income	354	274	268
Change in other comprehensive income (loss), net of tax	72	(4)	(61)
Realized gain on sale of life affiliate, net of tax			8
Net purchase of treasury stock	(17)		(154)
Dividends declared:
Balance, end of period	6,676		6,293
Class A
Dividends declared:
Dividends declared	(26)		(101)
Class B
Dividends declared:
Dividends declared	0		(1)
Indemnity
Reconciliation of the beginning and ending balances of shareholders' equity and noncontrolling interest
Balance, beginning of period	781	912	912
Net income			169
Change in other comprehensive income (loss), net of tax	2		(52)
Realized gain on sale of life affiliate, net of tax			8
Net purchase of treasury stock	(17)		(154)
Dividends declared:
Balance, end of period	776		781
Indemnity | Class A
Dividends declared:
Dividends declared (in dollars per share)	$ 0.5525	$ 0.515	$ 2.0975
Dividends declared	(26)		(101)
Indemnity | Class B
Dividends declared:
Dividends declared (in dollars per share)	$ 82.875	$ 77.25	$ 314.6250
Dividends declared	0		(1)
Exchange
Reconciliation of the beginning and ending balances of shareholders' equity and noncontrolling interest
Balance, beginning of period	5,512	5,422	5,422
Net income	318		99
Change in other comprehensive income (loss), net of tax	70		(9)
Dividends declared:
Balance, end of period	$ 5,900		$ 5,512