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]	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjusted Balance	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, 2019		$ 11,121	$ (3,754)	$ 11,203	$ 36,142	$ (63)	$ 36,079	$ 2,543	$ (1,939)	$ 15
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 benefit of $401 and $324								(2,155)
Amounts reclassified from AOCI, net of income tax (expense) benefit of $4 and $(40)								279
Change in period, net of income tax benefit of $405 and $284								(1,876)
Change in period, net of income tax benefit of $2 and $34									(825)
Change in period, net of income tax benefit of $5 and $3										(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)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(40)							(40)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax								284
OCI, Debt Securities, Available-for-Sale, Gain (Loss), before Adjustment, Tax								324
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax									34
Pension liability adjustment, Change in period, income tax (expense) benefit										3
Balance - beginning of period at Dec. 31, 2020	59,441	11,064	(3,644)	9,815	39,337	$ 0	$ 39,337	4,673	(1,637)	(167)
Common Shares repurchased			(519)
Net shares redeemed under employee share-based compensation plans			262	(187)
Exercise of stock options				(24)
Share-based compensation expense				66
Adjustments to Additional Paid in Capital, Dividends in Excess of Retained Earnings				(352)
Net income (loss)	2,300				2,300
Funding of dividends declared from Additional paid-in capital					352
Dividends declared on Common Shares					(352)
Change in period, before reclassification from AOCI, net of income tax benefit of $401 and $324								(1,892)
Amounts reclassified from AOCI, net of income tax (expense) benefit of $4 and $(40)								(20)
Change in period, net of income tax benefit of $405 and $284								(1,912)
Change in period, net of income tax benefit of $2 and $34									24
Change in period, net of income tax benefit of $5 and $3										(23)
Balance - end of period at Mar. 31, 2021	59,076	$ 11,064	$ (3,901)	$ 9,318	$ 41,637			2,761	(1,613)	(190)	$ 958
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	$ 4							4
Other Comprehensive Income (Loss), Securities, Available-for-sale, Tax								405
OCI, Debt Securities, Available-for-Sale, Gain (Loss), before Adjustment, Tax								$ 401
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax									$ 2
Pension liability adjustment, Change in period, income tax (expense) benefit										$ 5
Accounting Standards Update [Extensible List]	Accounting Standards Update 2016-13 [Member]