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					$ 409	$ (416)
Balance - beginning of period at Dec. 31, 2017		$ 11,121	$ (1,944)	$ 13,978	27,883	1,034	$ (1,187)	$ 280
Balance - beginning of period (Previous Accounting Guidance [Member]) at Dec. 31, 2017					27,474	1,450
Common Shares repurchased			0
Net shares redeemed under employee share-based compensation plans			217	(262)
Exercise of stock options				(16)
Share-based compensation expense				62
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(332)
Net income (loss)	$ 1,082				1,082
Funding of dividends declared from Additional paid-in capital					332
Dividends declared on Common Shares					(332)
Change in period, before reclassification from AOCI, net of income tax benefit (expense) of $(324) and $226						(1,008)
Amounts reclassified from AOCI, net of income tax expense of $(6) and $(3)						20
Change in period, net of income tax benefit (expense) of $(330) and $223						(988)
Change in period, net of income tax expense of $(7) and $(19)							378
Change in period, net of income tax benefit of $6 and $4								(19)
Balance - end of period at Mar. 31, 2018	51,287	11,121	(1,727)	13,430	28,965	46	(809)	261	$ (502)
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			(367)
Net shares redeemed under employee share-based compensation plans			210	(191)
Exercise of stock options				(34)
Share-based compensation expense				54
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(335)
Net income (loss)	1,040				1,040
Funding of dividends declared from Additional paid-in capital					335
Dividends declared on Common Shares					(335)
Change in period, before reclassification from AOCI, net of income tax benefit (expense) of $(324) and $226						1,521
Amounts reclassified from AOCI, net of income tax expense of $(6) and $(3)						38
Change in period, net of income tax benefit (expense) of $(330) and $223						1,559
Change in period, net of income tax expense of $(7) and $(19)							140
Change in period, net of income tax benefit of $6 and $4								(21)
Balance - end of period at Mar. 31, 2019	$ 52,355	$ 11,121	$ (2,775)	$ 12,051	$ 32,728	$ 1,014	$ (1,836)	$ 52	$ (770)