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]
Balance - beginning of period at Dec. 31, 2018		$ 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
Balance - beginning of period (Accounting Standards Update 2017-08 [Member]) at Dec. 31, 2018					(12)
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 (expense) benefit of $324 and $(324)						1,521
Amounts reclassified from AOCI, net of income tax expense of $(40) and $(6)						38
Change in period, net of income tax (expense) benefit of $284 and $(330)						1,559
Change in period, net of income tax (expense) benefit of $34 and $(7)							140
Change in period, net of income tax benefit of $3 and $6								(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)
Balance - beginning of period at Dec. 31, 2019	55,331	11,121	(3,754)	11,203	36,079	2,543	(1,939)	15
Balance - beginning of period (Previous Accounting Guidance [Member]) at Dec. 31, 2019					36,142
Balance - beginning of period (Accounting Standards Update 2016-13 [Member]) at Dec. 31, 2019					(63)
Common Shares repurchased			(326)
Net shares redeemed under employee share-based compensation plans			208	(196)
Exercise of stock options				(26)
Share-based compensation expense				69
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(340)
Net income (loss)	252				252
Funding of dividends declared from Additional paid-in capital					(340)
Dividends declared on Common Shares					(340)
Change in period, before reclassification from AOCI, net of income tax (expense) benefit of $324 and $(324)						(2,155)
Amounts reclassified from AOCI, net of income tax expense of $(40) and $(6)						279
Change in period, net of income tax (expense) benefit of $284 and $(330)						(1,876)
Change in period, net of income tax (expense) benefit of $34 and $(7)							(825)
Change in period, net of income tax benefit of $3 and $6								(11)
Balance - end of period at Mar. 31, 2020	$ 52,197	$ 11,121	$ (3,872)	$ 10,710	36,331	$ 667	$ (2,764)	$ 4	$ (2,093)
Balance - end of period (Accounting Standards Update 2016-13 [Member]) at Mar. 31, 2020					$ (63)