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, 2012		$ 9,591	$ (159)	$ 5,179	$ 10,033		$ 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
Funding of dividends declared from Additional paid-in capital				0
Change in year, before reclassification from AOCI, net of income tax benefit (expense) of $154, $(176) and $391							(1,371)
Amounts reclassified from AOCI, net of income tax benefit (expense) of $(2), $9 and $17							(88)
Change in year, net of income tax benefit (expense) of $152, $(167), and $408							(1,459)
Change in year, net of income tax benefit (expense) of nil, $(12), and $63								(276)
Change in year, net of income tax benefit (expense) of $(6), $4, and nil									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 $154, $(176) and $391							644
Amounts reclassified from AOCI, net of income tax benefit (expense) of $(2), $9 and $17							33
Change in year, net of income tax benefit (expense) of $152, $(167), and $408							677
Change in year, net of income tax benefit (expense) of nil, $(12), and $63								(644)
Change in year, net of income tax benefit (expense) of $(6), $4, and nil									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)
Net shares redeemed under employee share-based compensation plans				(160)
Exercise of stock options				(61)
Dividends declared on Common Shares – par value reduction		(222)
Common Shares repurchased			(734)
Net shares redeemed under employee share-based compensation plans			260
Share-based compensation expense and other				184
Tax benefit on share-based compensation expense				26
Net income	2,834				2,834
Funding of dividends declared from Additional paid-in capital				(653)	653
Dividends declared on Common Shares					(653)
Change in year, before reclassification from AOCI, net of income tax benefit (expense) of $154, $(176) and $391							(1,126)
Amounts reclassified from AOCI, net of income tax benefit (expense) of $(2), $9 and $17							149
Change in year, net of income tax benefit (expense) of $152, $(167), and $408							(977)
Change in year, net of income tax benefit (expense) of nil, $(12), and $63								(958)
Change in year, net of income tax benefit (expense) of $(6), $4, and nil									9
Balance - end of year at Dec. 31, 2015	$ 29,135	$ 7,833	$ (1,922)	$ 4,481	$ 19,478	$ (735)	$ 874	$ (1,539)	$ (70)