Consolidated Statements of Shareholders' Equity (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Stockholders Equity [Abstract]
Common treasury shares (in shares)	45,243,329	45,813,109	46,292,384	38,308,825
Tax on foreign currency translation	$ 4	$ 4	$ (10)
Tax on amortization of prior service cost and unrecognized gains and losses included in total benefit cost	35	33	34
Tax on (increase)/decrease in net actuarial losses	(10)	(42)	1
Tax on immediate recognition of prior service cost and unrecognized gains and losses due to curtailments, settlements, and divestitures	7	2	5
Prior service (cost) credit from plan amendments, tax	(1)	1	(3)
Tax effect of deferred derivative gains (losses)	0	0	3
Tax effect of reclassification adjustment for amounts recognized in income	$ 0	$ 0	$ 0
Cash dividends declared per common share (in dollars per share)	$ 0.16	$ 0.64	$ 0.58