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]
Balance - beginning of period at Dec. 31, 2016		$ 11,121	$ (1,480)	$ 15,335	$ 23,613	$ 1,058	$ (1,663)	$ 291
Common Shares repurchased			(707)
Net shares redeemed under employee share-based compensation plans			310	(311)
Exercise of stock options				(43)
Share-based compensation expense				223
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(987)
Net income (loss)	$ 2,328				2,328
Funding of dividends declared from Additional paid-in capital					987
Dividends declared on Common Shares					(987)
Change in period, before reclassification from AOCI, net of income tax benefit (expense) of $358 and $(310)						609
Amounts reclassified from AOCI, net of income tax benefit (expense) of $(19) and $3						(24)
Change in period, net of income tax benefit (expense) of $339 and $(307)						585
Change in period, net of income tax benefit (expense) of $5 and $(14)							887
Change in period, net of income tax benefit of $12 and $29								(89)
Balance - end of period at Sep. 30, 2017	50,471	11,121	(1,877)	14,217	25,941	1,643	(776)	202	$ 1,069
Cumulative effect of adoption of accounting guidance (refer to Note 1)					410	(417)
Balance - beginning of period at Dec. 31, 2017	51,172	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 $358 and $(310)						(1,705)
Amounts reclassified from AOCI, net of income tax benefit (expense) of $(19) and $3						123
Change in period, net of income tax benefit (expense) of $339 and $(307)						(1,582)
Change in period, net of income tax benefit (expense) of $5 and $(14)							(654)
Change in period, net of income tax benefit of $12 and $29								(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)