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]	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]
Cumulative effect of adoption of accounting guidance					$ 410	$ (417)
Balance - beginning of period at Dec. 31, 2017		$ 11,121	$ (1,944)	$ 13,978	27,884	1,033	$ (1,187)	$ 280
Balance - beginning of period (Previous Accounting Guidance [Member]) at Dec. 31, 2017					27,474	1,450
Common Shares repurchased			(703)
Net shares redeemed under employee share-based compensation plans			275	(261)
Exercise of stock options				(42)
Share-based compensation expense				186
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(1,008)
Net income (loss)	$ 3,607				3,607
Funding of dividends declared from Additional paid-in capital					1,008
Dividends declared on Common Shares					(1,008)
Change in period, before reclassification from AOCI, net of income tax benefit (expense) of $(125), $58, $(674) and $358						(1,705)
Amounts reclassified from AOCI, net of income tax benefit (expense) of nil, $(4), $(2) and $(19)						123
Change in period, net of income tax benefit (expense) of $(125), $54, $(676) and $339						(1,582)
Change in period, net of income tax benefit of $8, $20, $3 and $5							(654)
Change in period, net of income tax benefit of $4, $3, $13 and $12								(49)
Balance - end of period at Sep. 30, 2018	50,934	11,121	(2,372)	12,853	31,491	(549)	(1,841)	231	$ (2,159)
Cumulative effect of adoption of accounting guidance					0	0
Balance - beginning of period at Jun. 30, 2018		11,121	(2,040)	13,150	30,260	(390)	(1,379)	249
Balance - beginning of period (Previous Accounting Guidance [Member]) at Jun. 30, 2018					30,260	(390)
Common Shares repurchased			(379)
Net shares redeemed under employee share-based compensation plans			47	0
Exercise of stock options				(23)
Share-based compensation expense				63
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(337)
Net income (loss)	1,231				1,231
Funding of dividends declared from Additional paid-in capital					337
Dividends declared on Common Shares					(337)
Change in period, before reclassification from AOCI, net of income tax benefit (expense) of $(125), $58, $(674) and $358						(193)
Amounts reclassified from AOCI, net of income tax benefit (expense) of nil, $(4), $(2) and $(19)						34
Change in period, net of income tax benefit (expense) of $(125), $54, $(676) and $339						(159)
Change in period, net of income tax benefit of $8, $20, $3 and $5							(462)
Change in period, net of income tax benefit of $4, $3, $13 and $12								(18)
Balance - end of period at Sep. 30, 2018	50,934	11,121	(2,372)	12,853	31,491	(549)	(1,841)	231	(2,159)
Cumulative effect of adoption of accounting guidance						0
Cumulative effect of adoption of accounting guidance | Accounting Standards Update 2017-08 [Member]					(12)
Balance - beginning of period at Dec. 31, 2018	50,312	11,121	(2,618)	12,557	31,688	(545)	(1,976)	73
Balance - beginning of period (Previous Accounting Guidance [Member]) at Dec. 31, 2018					31,700	(545)
Common Shares repurchased			(1,221)
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 benefit (expense) of $(125), $58, $(674) and $358						3,117
Amounts reclassified from AOCI, net of income tax benefit (expense) of nil, $(4), $(2) and $(19)						41
Change in period, net of income tax benefit (expense) of $(125), $54, $(676) and $339						3,158
Change in period, net of income tax benefit of $8, $20, $3 and $5							(140)
Change in period, net of income tax benefit of $4, $3, $13 and $12								(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
Cumulative effect of adoption of accounting guidance						0
Cumulative effect of adoption of accounting guidance | Accounting Standards Update 2017-08 [Member]					0
Balance - beginning of period at Jun. 30, 2019		11,121	(3,093)	11,757	33,878	2,033	(1,931)	37
Balance - beginning of period (Previous Accounting Guidance [Member]) at Jun. 30, 2019					33,878	2,033
Common Shares repurchased			(478)
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 benefit (expense) of $(125), $58, $(674) and $358						569
Amounts reclassified from AOCI, net of income tax benefit (expense) of nil, $(4), $(2) and $(19)						11
Change in period, net of income tax benefit (expense) of $(125), $54, $(676) and $339						580
Change in period, net of income tax benefit of $8, $20, $3 and $5							(185)
Change in period, net of income tax benefit of $4, $3, $13 and $12								(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