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 2016-13 [Member]) at Dec. 31, 2018					(12)
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 expense of $(522), $(225), $(198) and $(549)						2,548
Amounts reclassified from AOCI, net of income tax (expense) benefit of $(2), $4, $(42) and $(2)						30
Change in period, net of income tax expense of $(524), $(221), $(240) and $(551)						2,578
Change in period, net of income tax (expense) benefit of $6, $2, $40 and $(5)							45
Change in period, net of income tax benefit of $5, $3, $8 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
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax						(549)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(2)					(2)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax						(551)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax							(5)
Pension liability adjustment, Change in period, income tax (expense) benefit								9
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
Balance - beginning of period (Accounting Standards Update 2017-08 [Member]) at Mar. 31, 2019					0
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 expense of $(522), $(225), $(198) and $(549)						1,027
Amounts reclassified from AOCI, net of income tax (expense) benefit of $(2), $4, $(42) and $(2)						(8)
Change in period, net of income tax expense of $(524), $(221), $(240) and $(551)						1,019
Change in period, net of income tax (expense) benefit of $6, $2, $40 and $(5)							(95)
Change in period, net of income tax benefit of $5, $3, $8 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
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax						(225)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	4					4
Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax						(221)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax							2
Pension liability adjustment, Change in period, income tax (expense) benefit								3
Balance - beginning of period at Dec. 31, 2019	55,331	11,121	(3,754)	11,203	36,070	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					(72)
Common Shares repurchased			(326)
Net shares redeemed under employee share-based compensation plans			214	(189)
Exercise of stock options				(29)
Share-based compensation expense				124
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(693)
Net income (loss)	(79)				(79)
Funding of dividends declared from Additional paid-in capital					693
Dividends declared on Common Shares					(693)
Change in period, before reclassification from AOCI, net of income tax expense of $(522), $(225), $(198) and $(549)						571
Amounts reclassified from AOCI, net of income tax (expense) benefit of $(2), $4, $(42) and $(2)						310
Change in period, net of income tax expense of $(524), $(221), $(240) and $(551)						881
Change in period, net of income tax (expense) benefit of $6, $2, $40 and $(5)							(374)
Change in period, net of income tax benefit of $5, $3, $8 and $9								(28)
Balance - end of period at Jun. 30, 2020	54,760	11,121	(3,866)	10,416	35,991	3,424	(2,313)	(13)	1,098
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax						(198)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(42)					(42)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax						(240)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax							40
Pension liability adjustment, Change in period, income tax (expense) benefit								8
Balance - beginning of period at Mar. 31, 2020		11,121	(3,872)	10,710	36,322	667	(2,764)	4
Balance - beginning of period (Previous Accounting Guidance [Member]) at Mar. 31, 2020					36,322
Balance - beginning of period (Accounting Standards Update 2016-13 [Member]) at Mar. 31, 2020					0
Common Shares repurchased			0
Net shares redeemed under employee share-based compensation plans			6	7
Exercise of stock options				(3)
Share-based compensation expense				55
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(353)
Net income (loss)	(331)				(331)
Funding of dividends declared from Additional paid-in capital					353
Dividends declared on Common Shares					(353)
Change in period, before reclassification from AOCI, net of income tax expense of $(522), $(225), $(198) and $(549)						2,726
Amounts reclassified from AOCI, net of income tax (expense) benefit of $(2), $4, $(42) and $(2)						31
Change in period, net of income tax expense of $(524), $(221), $(240) and $(551)						2,757
Change in period, net of income tax (expense) benefit of $6, $2, $40 and $(5)							451
Change in period, net of income tax benefit of $5, $3, $8 and $9								(17)
Balance - end of period at Jun. 30, 2020	54,760	$ 11,121	$ (3,866)	$ 10,416	$ 35,991	3,424	(2,313)	(13)	$ 1,098
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax						(522)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	$ (2)					(2)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax						$ (524)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax							$ 6
Pension liability adjustment, Change in period, income tax (expense) benefit								$ 5