Consolidated Statements Of Shareholders' Equity (USD $) In Millions, unless otherwise specified	Common Shares [Member]	Common Shares In Treasury [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Deferred Compensation Obligation [Member]	Net Unrealized Appreciation (Depreciation) On Investments [Member]	Cumulative Translation Adjustment [Member]	Pension Liability Adjustment [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Common Shares Issued To Employee Trust [Member]	Total
Balance - beginning of period at Dec. 31, 2008	$ 10,827	$ (3)	$ 5,464	$ 74	$ 3	$ (1,712)	$ (161)	$ (43)		$ (3)
Net shares issued (redeemed) under employee share-based compensation plans	73		(77)
Exercise of stock options	5		10
Dividends on Common Shares-par value reduction	(402)
Share-based compensation expense and other			121
Tax (expense) benefit on share-based compensation expense			8								8
Effect of adoption of OTTI standard				195		(242)
Net income				2,549							2,549
Decrease to obligation					(1)
Accumulated other comprehensive income (loss)
Change in year, net of income tax expense of $(157), $(152), and $(481)						2,611
Change in year, net of income tax (expense) benefit of $1, $29, and $(167)							401
Change in year, net of income tax (expense) benefit of $(3), $(4), and $17								(31)
Decrease in Common Shares										1
Balance - end of period at Dec. 31, 2009	10,503	(3)	5,526	2,818	2	657	240	(74)	823	(2)	19,667
Net shares issued (redeemed) under employee share-based compensation plans	71		(64)
Exercise of stock options	30		23
Common Shares repurchased		(303)
Dividends on Common Shares-par value reduction	(443)
Other Common Shares issued in treasury, net of net shares redeemed under employee share-based compensation plans		(24)
Share-based compensation expense and other			139
Tax (expense) benefit on share-based compensation expense			(1)								(1)
Net income				3,108							3,108
Accumulated other comprehensive income (loss)
Change in year, net of income tax expense of $(157), $(152), and $(481)						742
Change in year, net of income tax (expense) benefit of $1, $29, and $(167)							22
Change in year, net of income tax (expense) benefit of $(3), $(4), and $17								7
Balance - end of period at Dec. 31, 2010	10,161	(330)	5,623	5,926	2	1,399	262	(67)	1,594	(2)	22,974
Net shares issued (redeemed) under employee share-based compensation plans			(104)
Exercise of stock options	47		16
Common Shares repurchased		(132)
Dividends on Common Shares-par value reduction	(113)
Other Common Shares issued in treasury, net of net shares redeemed under employee share-based compensation plans		135
Share-based compensation expense and other			139
Tax (expense) benefit on share-based compensation expense			6								6
Funding of dividends to Retained earnings			(354)
Net income				1,585							1,585
Funding of dividends from Additional paid-in capital				354
Dividends on Common Shares				(354)
Decrease to obligation					(2)
Accumulated other comprehensive income (loss)
Change in year, net of income tax expense of $(157), $(152), and $(481)						316
Change in year, net of income tax (expense) benefit of $1, $29, and $(167)							(4)
Change in year, net of income tax (expense) benefit of $(3), $(4), and $17								5
Decrease in Common Shares										2
Balance - end of period at Dec. 31, 2011	$ 10,095	$ (327)	$ 5,326	$ 7,511		$ 1,715	$ 258	$ (62)	$ 1,911		$ 24,516