Reconciliation of Shareholders' Equity (Details) (USD $) In Millions, except Per Share data	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Reconciliation of shareholders' equity
Balance at the beginning of the period			$ 6,334	$ 5,725	$ 5,725
Comprehensive income:
Net income (loss)	(180)	275	(13)	406	660
Other comprehensive income, net of tax:
Unrealized gains (loss) on securities			(15)		110
Reclassification of unrealized gain on sale of affiliated subsidiaries			(9)		(15)
Postretirement plans:
Amortization of prior service cost					0
Amortization of net actuarial loss					2
Net actuarial loss during year					(6)
Loss due to plan changes during year					0
Curtailment/settlement loss arising during year					0
Postretirement plans					(4)
Other comprehensive (loss) income, net of tax	(37)	133	(24)	215	91
Reclassification of unrealized gain on sale of affiliated subsidiaries			9		15
Comprehensive income (loss)	(217)	408	(28)	621	766
Purchase of treasury stock			(131)		(58)
Dividends declared:
Balance at the end of the period	6,098		6,098		6,334
Class A | Indemnity
Dividends declared:
Dividends declared (in dollars per share)	$ 0.515	$ 0.48	$ 1.545	$ 1.44	$ 1.995
Total dividends declared			(77)		(99)
Class B | Indemnity
Dividends declared:
Dividends declared (in dollars per share)	$ 77.25	$ 72.00	$ 231.750	$ 216.000	$ 293.250
Total dividends declared			0		0
Indemnity
Reconciliation of shareholders' equity
Balance at the beginning of the period			912	902	902
Comprehensive income:
Net income (loss)	47	54	143	150	162
Other comprehensive income, net of tax:
Unrealized gains (loss) on securities			(2)		9
Reclassification of unrealized gain on sale of affiliated subsidiaries			(9)		(15)
Postretirement plans:
Amortization of prior service cost					0
Amortization of net actuarial loss					2
Net actuarial loss during year					(6)
Loss due to plan changes during year					0
Curtailment/settlement loss arising during year					0
Postretirement plans					(4)
Other comprehensive (loss) income, net of tax	(1)	15	(11)	26	(10)
Reclassification of unrealized gain on sale of affiliated subsidiaries			9		15
Comprehensive income	46	69	141	176	167
Purchase of treasury stock			(131)		(58)
Dividends declared:
Balance at the end of the period	845		845		912
Exchange
Reconciliation of shareholders' equity
Balance at the beginning of the period			5,422	4,823	4,823
Comprehensive income:
Net income (loss)			(156)		498
Other comprehensive income, net of tax:
Unrealized gains (loss) on securities			(13)		101
Postretirement plans:
Other comprehensive (loss) income, net of tax	(36)	118	(13)	189	101
Comprehensive income (loss)	(263)	339	(169)	445	599
Dividends declared:
Balance at the end of the period	5,253		5,253		5,422
Class A
Dividends declared:
Total dividends declared			(77)		(99)
Class B
Dividends declared:
Total dividends declared			$ 0		$ 0