Consolidated Statements Of Shareholders' Equity (USD $) In Millions	Total	Common Shares	Common Shares in Treasury	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income	Net unrealized appreciation on investments	Cumulative Translation Adjustment	Accumulated Defined Benefit Plans Adjustment [Member]
Balance – beginning of year at Dec. 31, 2011		$ 10,095	$ (327)	$ 5,326	$ 7,327		$ 1,715	$ 258	$ (62)
Net shares redeemed under employee share-based compensation plans				(93)
Exercise of stock options				(7)
Dividends declared on Common Shares – par value reduction		(504)
Common Shares repurchased			(7)
Net shares redeemed under employee share-based compensation plans			175
Share-based compensation expense and other				135
Tax benefit on share-based compensation expense				18
Net income	2,706				2,706
Funding of dividends declared from Additional paid-in capital				(200)	200
Dividends declared on Common Shares					(200)
Change in year, net of income tax benefit (expense) of $(167), $408, and $(198)							918
Change in year, net of income tax benefit (expense) of $(12), $63, and $(35)								81
Change in year, net of income tax benefit of $4, nil, and $12									(23)
Balance - end of year at Dec. 31, 2012	27,531	9,591	(159)	5,179	10,033	2,887	2,633	339	(85)
Net shares redeemed under employee share-based compensation plans				(126)
Exercise of stock options				(42)
Dividends declared on Common Shares – par value reduction		(692)
Common Shares repurchased			(290)
Net shares redeemed under employee share-based compensation plans			194
Share-based compensation expense and other				191
Tax benefit on share-based compensation expense				36
Net income	3,758				3,758
Change in year, before reclassification from AOCI, net of income tax benefit (expense) of $(176) and $391							(1,371)
Amounts reclassified from AOCI, net of income tax benefit of $9 and $17							(88)
Change in year, net of income tax benefit (expense) of $(167), $408, and $(198)							(1,459)
Change in year, net of income tax benefit (expense) of $(12), $63, and $(35)								(276)
Change in year, net of income tax benefit of $4, nil, and $12									0
Balance - end of year at Dec. 31, 2013	28,825	8,899	(255)	5,238	13,791	1,152	1,174	63	(85)
Net shares redeemed under employee share-based compensation plans				(167)
Exercise of stock options				(58)
Dividends declared on Common Shares – par value reduction		(844)
Common Shares repurchased			(1,449)
Net shares redeemed under employee share-based compensation plans			256
Share-based compensation expense and other				185
Tax benefit on share-based compensation expense				28
Net income	2,853				2,853
Funding of dividends declared from Additional paid-in capital				(81)	81
Dividends declared on Common Shares					(81)
Change in year, before reclassification from AOCI, net of income tax benefit (expense) of $(176) and $391							644
Amounts reclassified from AOCI, net of income tax benefit of $9 and $17							33
Change in year, net of income tax benefit (expense) of $(167), $408, and $(198)							677
Change in year, net of income tax benefit (expense) of $(12), $63, and $(35)								(644)
Change in year, net of income tax benefit of $4, nil, and $12									6
Balance - end of year at Dec. 31, 2014	$ 29,587	$ 8,055	$ (1,448)	$ 5,145	$ 16,644	$ 1,191	$ 1,851	$ (581)	$ (79)