Consolidated Statements Of Shareholders' Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Common shares in treasury [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjusted Balance	AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]	Cumulative Foreign Currency Translation Adjustment [Member]	Postretirement Benefit Liability Adjustment [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance - beginning of period at Dec. 31, 2019		$ 11,121	$ (3,754)	$ 11,203	$ 36,142	$ (72)	$ 36,070	$ 2,543	$ (1,939)	$ 15
Common Shares repurchased			(326)
Treasury Stock, Retired, Cost Method, Amount		(57)	323		(266)
Net shares redeemed under employee share-based compensation plans			216	(195)
Exercise of stock options				(30)
Share-based compensation expense				183
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(1,046)
Net income (loss)	$ 1,115				1,115
Funding of dividends declared from Additional paid-in capital					1,046
Dividends declared on Common Shares					(1,046)
Change in period, before reclassification from AOCI, net of income tax (expense) benefit of $101, $(102), $395 and $(300)								1,156
Amounts reclassified from AOCI, net of income tax (expense) benefit of $(3), $7, $(5), $(35)								268
Change in period, net of income tax (expense) benefit of $98, $(95), $390 and $(335)								1,424
Change in period, net of income tax (expense) benefit of $23, $(13), $7 and $27									(141)
Change in period, net of income tax (expense) benefit of $(1), $5, $6 and $13										(46)
Balance - end of period at Sep. 30, 2020	56,413	11,064	(3,541)	10,115	36,919			3,967	(2,080)	(31)	$ 1,856
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(35)							(35)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax								(335)
OCI, Debt Securities, Available-for-Sale, Gain (Loss), before Adjustment, Tax								(300)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax									27
Pension liability adjustment, Change in period, income tax (expense) benefit										13
Balance - beginning of period at Jun. 30, 2020		11,121	(3,866)	10,416	35,991	0	35,991	3,424	(2,313)	(13)
Common Shares repurchased			0
Treasury Stock, Retired, Cost Method, Amount		(57)	323		(266)
Net shares redeemed under employee share-based compensation plans			2	(6)
Exercise of stock options				(1)
Share-based compensation expense				59
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(353)
Net income (loss)	1,194				1,194
Funding of dividends declared from Additional paid-in capital					353
Dividends declared on Common Shares					(353)
Change in period, before reclassification from AOCI, net of income tax (expense) benefit of $101, $(102), $395 and $(300)								585
Amounts reclassified from AOCI, net of income tax (expense) benefit of $(3), $7, $(5), $(35)								(42)
Change in period, net of income tax (expense) benefit of $98, $(95), $390 and $(335)								543
Change in period, net of income tax (expense) benefit of $23, $(13), $7 and $27									233
Change in period, net of income tax (expense) benefit of $(1), $5, $6 and $13										(18)
Balance - end of period at Sep. 30, 2020	56,413	11,064	(3,541)	10,115	36,919			3,967	(2,080)	(31)	1,856
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	7							7
Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax								(95)
OCI, Debt Securities, Available-for-Sale, Gain (Loss), before Adjustment, Tax								(102)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax									(13)
Pension liability adjustment, Change in period, income tax (expense) benefit										5
Balance - beginning of period at Dec. 31, 2020	59,441	11,064	(3,644)	9,815	39,337	0	39,337	4,673	(1,637)	(167)
Common Shares repurchased			(3,956)
Treasury Stock, Retired, Cost Method, Amount		(79)	590		(511)
Net shares redeemed under employee share-based compensation plans			389	(184)
Exercise of stock options				(45)
Share-based compensation expense				216
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(1,050)
Net income (loss)	6,398				6,398
Funding of dividends declared from Additional paid-in capital					1,050
Dividends declared on Common Shares					(1,050)
Change in period, before reclassification from AOCI, net of income tax (expense) benefit of $101, $(102), $395 and $(300)								(1,756)
Amounts reclassified from AOCI, net of income tax (expense) benefit of $(3), $7, $(5), $(35)								(31)
Change in period, net of income tax (expense) benefit of $98, $(95), $390 and $(335)								(1,787)
Change in period, net of income tax (expense) benefit of $23, $(13), $7 and $27									(77)
Change in period, net of income tax (expense) benefit of $(1), $5, $6 and $13										(27)
Balance - end of period at Sep. 30, 2021	59,318	10,985	(6,621)	8,752	45,224			2,886	(1,714)	(194)	978
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	$ (5)							(5)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax								390
OCI, Debt Securities, Available-for-Sale, Gain (Loss), before Adjustment, Tax								395
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax									7
Pension liability adjustment, Change in period, income tax (expense) benefit										6
Accounting Standards Update [Extensible List]	Accounting Standards Update 2016-13 [Member]
Balance - beginning of period at Jun. 30, 2021		11,064	(5,772)	9,046	43,902	$ 0	$ 43,902	3,342	(1,323)	(197)
Common Shares repurchased			(1,516)
Treasury Stock, Retired, Cost Method, Amount		(79)	590		(511)
Net shares redeemed under employee share-based compensation plans			77	(2)
Exercise of stock options				(15)
Share-based compensation expense				69
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(346)
Net income (loss)	$ 1,833				1,833
Funding of dividends declared from Additional paid-in capital					346
Dividends declared on Common Shares					(346)
Change in period, before reclassification from AOCI, net of income tax (expense) benefit of $101, $(102), $395 and $(300)								(463)
Amounts reclassified from AOCI, net of income tax (expense) benefit of $(3), $7, $(5), $(35)								7
Change in period, net of income tax (expense) benefit of $98, $(95), $390 and $(335)								(456)
Change in period, net of income tax (expense) benefit of $23, $(13), $7 and $27									(391)
Change in period, net of income tax (expense) benefit of $(1), $5, $6 and $13										3
Balance - end of period at Sep. 30, 2021	59,318	$ 10,985	$ (6,621)	$ 8,752	$ 45,224			2,886	(1,714)	(194)	$ 978
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	$ (3)							(3)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax								98
OCI, Debt Securities, Available-for-Sale, Gain (Loss), before Adjustment, Tax								$ 101
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax									$ 23
Pension liability adjustment, Change in period, income tax (expense) benefit										$ (1)