Consolidated Statements Of Shareholders' Equity - USD ($) $ in Millions	Total	Common Shares	Common Shares in Treasury	Additional Paid-in Capital	Retained Earnings	Net unrealized appreciation on investments	Cumulative Translation Adjustment	Accumulated Defined Benefit Plans Adjustment [Member]	Accumulated Other Comprehensive Income
Cumulative Effect of New Accounting Principle in Period of Adoption					$ 0	$ 0
Balance – beginning and end of year at Dec. 31, 2016		$ 11,121	$ (1,480)	$ 15,335	23,613	1,058	$ (1,663)	$ 291
Common Shares repurchased			(830)
Net shares redeemed under employee share-based compensation plans			366	(313)
Stock Issued During Period, Value, Stock Options Exercised				(58)
Share-based compensation expense				331
FundingDividendsDeclaredToRetainedEarnings				(1,317)
Net income	$ 3,861				3,861
Funding Dividends Declared From Additional Paid In Capital					1,317
Dividends declared on Common Shares					(1,317)
Change in year, before reclassification from AOCI, net of income tax (expense) benefit of $(647), $338, and $(228)						390
Amounts reclassified from AOCI, net of income tax (expense) benefit of nil, $(41), and $(13)						2
Change in year, net of income tax (expense) benefit of $(647), $297, and $(241)						392
Change in year, net of income tax benefit of $24, $35, and $5							476
Change in year, net of income tax benefit of $18, $67, and $5								(11)
Balance – Ending of year at Dec. 31, 2017	51,172	11,121	(1,944)	13,978	27,738	1,154	(1,209)	327	$ 543
Balance – Ending of year (Previous Accounting Guidance [Member]) at Dec. 31, 2017					27,474	1,450	(1,187)	280
Cumulative Effect of New Accounting Principle in Period of Adoption					264	(296)
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2018-02 [Member]							0	0
Common Shares repurchased			(1,021)
Net shares redeemed under employee share-based compensation plans			347	(313)
Stock Issued During Period, Value, Stock Options Exercised				(49)
Share-based compensation expense				285
FundingDividendsDeclaredToRetainedEarnings				(1,344)
Net income	3,962				3,962
Funding Dividends Declared From Additional Paid In Capital					1,344
Dividends declared on Common Shares					(1,344)
Change in year, before reclassification from AOCI, net of income tax (expense) benefit of $(647), $338, and $(228)						(1,960)
Amounts reclassified from AOCI, net of income tax (expense) benefit of nil, $(41), and $(13)						261
Change in year, net of income tax (expense) benefit of $(647), $297, and $(241)						(1,699)
Change in year, net of income tax benefit of $24, $35, and $5							(767)
Change in year, net of income tax benefit of $18, $67, and $5								(254)
Balance – Ending of year at Dec. 31, 2018	50,312	11,121	(2,618)	12,557	31,688	(545)	(1,976)	73	(2,448)
Balance – Ending of year (Previous Accounting Guidance [Member]) at Dec. 31, 2018					31,700	(545)	(1,976)	73
Cumulative Effect of New Accounting Principle in Period of Adoption					(12)
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2018-02 [Member]							(22)	47
Common Shares repurchased			(1,531)
Net shares redeemed under employee share-based compensation plans			395	(178)
Stock Issued During Period, Value, Stock Options Exercised				(82)
Share-based compensation expense				266
FundingDividendsDeclaredToRetainedEarnings				(1,360)
Net income	4,454				4,454
Funding Dividends Declared From Additional Paid In Capital					1,360
Dividends declared on Common Shares					(1,360)
Change in year, before reclassification from AOCI, net of income tax (expense) benefit of $(647), $338, and $(228)						3,057
Amounts reclassified from AOCI, net of income tax (expense) benefit of nil, $(41), and $(13)						31
Change in year, net of income tax (expense) benefit of $(647), $297, and $(241)						3,088
Change in year, net of income tax benefit of $24, $35, and $5							37
Change in year, net of income tax benefit of $18, $67, and $5								(58)
Balance – Ending of year at Dec. 31, 2019	$ 55,331	$ 11,121	$ (3,754)	$ 11,203	$ 36,142	2,543	(1,939)	15	$ 619
Cumulative Effect of New Accounting Principle in Period of Adoption						$ 0
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2018-02 [Member]							$ 0	$ 0