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, 2018		$ 11,121	$ (2,618)	$ 12,557	$ 31,700	$ (12)	$ 31,688	$ (545)	$ (1,976)	$ 73
Common Shares repurchased			(1,221)
Treasury Stock, Retired, Cost Method, Amount		0	0		0
Net shares redeemed under employee share-based compensation plans			335	(184)
Exercise of stock options				(65)
Share-based compensation expense				177
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(1,020)
Net income (loss)	$ 3,281				3,281
Funding of dividends declared from Additional paid-in capital					1,020
Dividends declared on Common Shares					(1,020)
Change in period, before reclassification from AOCI, net of income tax expense of $(102), $(125), $(300) and $(674)								3,117
Amounts reclassified from AOCI, net of income tax (expense) benefit of $7, nil, $(35) and $(2)								41
Change in period, net of income tax expense of $(95), $(125), $(335) and $(676)								3,158
Change in period, net of income tax (expense) benefit of $(13), $8, $27 and $3									(140)
Change in period, net of income tax benefit of $5, $4, $13 and $13										(49)
Balance - end of period at Sep. 30, 2019	54,572	11,121	(3,504)	11,465	34,969			2,613	(2,116)	24	$ 521
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax								(674)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(2)							(2)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax								(676)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax									3
Pension liability adjustment, Change in period, income tax (expense) benefit										13
Balance - beginning of period at Jun. 30, 2019		11,121	(3,093)	11,757	33,878	0	33,878	2,033	(1,931)	37
Common Shares repurchased			(478)
Treasury Stock, Retired, Cost Method, Amount		0	0		0
Net shares redeemed under employee share-based compensation plans			67	6
Exercise of stock options				(17)
Share-based compensation expense				60
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(341)
Net income (loss)	1,091				1,091
Funding of dividends declared from Additional paid-in capital					341
Dividends declared on Common Shares					(341)
Change in period, before reclassification from AOCI, net of income tax expense of $(102), $(125), $(300) and $(674)								569
Amounts reclassified from AOCI, net of income tax (expense) benefit of $7, nil, $(35) and $(2)								11
Change in period, net of income tax expense of $(95), $(125), $(335) and $(676)								580
Change in period, net of income tax (expense) benefit of $(13), $8, $27 and $3									(185)
Change in period, net of income tax benefit of $5, $4, $13 and $13										(13)
Balance - end of period at Sep. 30, 2019	54,572	11,121	(3,504)	11,465	34,969			2,613	(2,116)	24	521
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax								(125)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	0							0
Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax								(125)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax									8
Pension liability adjustment, Change in period, income tax (expense) benefit										4
Balance - beginning of period at Dec. 31, 2019	55,331	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 of $(102), $(125), $(300) and $(674)								1,156
Amounts reclassified from AOCI, net of income tax (expense) benefit of $7, nil, $(35) and $(2)								268
Change in period, net of income tax expense of $(95), $(125), $(335) and $(676)								1,424
Change in period, net of income tax (expense) benefit of $(13), $8, $27 and $3									(141)
Change in period, net of income tax benefit of $5, $4, $13 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), Available-for-sale Securities, before Reclassification Adjustments, Tax								(300)
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)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax									27
Pension liability adjustment, Change in period, income tax (expense) benefit										13
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
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 of $(102), $(125), $(300) and $(674)								585
Amounts reclassified from AOCI, net of income tax (expense) benefit of $7, nil, $(35) and $(2)								(42)
Change in period, net of income tax expense of $(95), $(125), $(335) and $(676)								543
Change in period, net of income tax (expense) benefit of $(13), $8, $27 and $3									233
Change in period, net of income tax benefit of $5, $4, $13 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), Available-for-sale Securities, before Reclassification Adjustments, Tax								(102)
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)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax									$ (13)
Pension liability adjustment, Change in period, income tax (expense) benefit										$ 5