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]	Accumulated Net Investment Gain (Loss) Attributable to 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			(324)
Net shares redeemed under employee share-based compensation plans			228	(261)
Exercise of stock options				(19)
Share-based compensation expense				123
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(671)
Net income (loss)	$ 2,376				2,376
Funding of dividends declared from Additional paid-in capital					671
Dividends declared on Common Shares					(671)
Change in period, before reclassification from AOCI, net of income tax benefit (expense) of $(225), $74, $(549) and $300						(1,512)
Amounts reclassified from AOCI, net of income tax benefit (expense) of $4, $(12), $(2) and $(15)						89
Change in period, net of income tax benefit (expense) of $(221), $62, $(551) and $285						(1,423)
Change in period, net of income tax benefit (expense) of $2, $4, $(5) and $(15)							(192)
Change in period, net of income tax benefit of $3, $5, $9 and $9								(31)
Balance - end of period at Jun. 30, 2018	50,971	11,121	(2,040)	13,150	30,260	(390)	(1,379)	249	$ (1,520)
Cumulative effect of adoption of accounting guidance					0	0
Balance - beginning of period at Mar. 31, 2018		11,121	(1,727)	13,430	28,966	45	(809)	261
Balance - beginning of period (Previous Accounting Guidance [Member]) at Mar. 31, 2018					28,966	45
Common Shares repurchased			(324)
Net shares redeemed under employee share-based compensation plans			11	1
Exercise of stock options				(3)
Share-based compensation expense				61
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(339)
Net income (loss)	1,294				1,294
Funding of dividends declared from Additional paid-in capital					339
Dividends declared on Common Shares					(339)
Change in period, before reclassification from AOCI, net of income tax benefit (expense) of $(225), $74, $(549) and $300						(504)
Amounts reclassified from AOCI, net of income tax benefit (expense) of $4, $(12), $(2) and $(15)						69
Change in period, net of income tax benefit (expense) of $(221), $62, $(551) and $285						(435)
Change in period, net of income tax benefit (expense) of $2, $4, $(5) and $(15)							(570)
Change in period, net of income tax benefit of $3, $5, $9 and $9								(12)
Balance - end of period at Jun. 30, 2018	50,971	11,121	(2,040)	13,150	30,260	(390)	(1,379)	249	(1,520)
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			(743)
Net shares redeemed under employee share-based compensation plans			268	(190)
Exercise of stock options				(48)
Share-based compensation expense				117
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(679)
Net income (loss)	2,190				2,190
Funding of dividends declared from Additional paid-in capital					679
Dividends declared on Common Shares					(679)
Change in period, before reclassification from AOCI, net of income tax benefit (expense) of $(225), $74, $(549) and $300						2,548
Amounts reclassified from AOCI, net of income tax benefit (expense) of $4, $(12), $(2) and $(15)						30
Change in period, net of income tax benefit (expense) of $(221), $62, $(551) and $285						2,578
Change in period, net of income tax benefit (expense) of $2, $4, $(5) and $(15)							45
Change in period, net of income tax benefit of $3, $5, $9 and $9								(36)
Balance - end of period at Jun. 30, 2019	53,802	11,121	(3,093)	11,757	33,878	2,033	(1,931)	37	139
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 Mar. 31, 2019		11,121	(2,775)	12,051	32,728	1,014	(1,836)	52
Balance - beginning of period (Previous Accounting Guidance [Member]) at Mar. 31, 2019					32,728	1,014
Common Shares repurchased			(376)
Net shares redeemed under employee share-based compensation plans			58	1
Exercise of stock options				(14)
Share-based compensation expense				63
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(344)
Net income (loss)	1,150				1,150
Funding of dividends declared from Additional paid-in capital					344
Dividends declared on Common Shares					(344)
Change in period, before reclassification from AOCI, net of income tax benefit (expense) of $(225), $74, $(549) and $300						1,027
Amounts reclassified from AOCI, net of income tax benefit (expense) of $4, $(12), $(2) and $(15)						(8)
Change in period, net of income tax benefit (expense) of $(221), $62, $(551) and $285						1,019
Change in period, net of income tax benefit (expense) of $2, $4, $(5) and $(15)							(95)
Change in period, net of income tax benefit of $3, $5, $9 and $9								(15)
Balance - end of period at Jun. 30, 2019	$ 53,802	$ 11,121	$ (3,093)	$ 11,757	$ 33,878	$ 2,033	$ (1,931)	$ 37	$ 139