Consolidated Statements of Shareholders' Equity (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Statement Of Stockholders Equity [Abstract]
Common treasury shares (in shares)	45,329,344	45,899,918	45,452,865	45,942,257	45,329,344	45,899,918	45,813,109	46,292,384
Tax on foreign currency translation	$ 2	$ (1)	$ (4)	$ 4	$ (2)	$ 3
Tax on amortization of prior service cost and unrecognized gains and losses included in total benefit cost	9	8	17	16	26	24
Tax on increase / decrease in net actuarial losses	(1)	(3)	(2)	4	(3)	1
Prior service (cost) credit from plan amendments, tax	0	0		0	0	0
Tax on immediate recognition of prior service cost and unrecognized gains and losses due to curtailments, settlements, and divestitures	4	0	(1)		3	0
Tax effect of deferred derivative gains	0	4	1	0	1	4
Tax effect of reclassification adjustment for amounts recognized in income	$ 0	$ 0	$ 0	$ (1)	$ 0	$ (1)
Cash dividends declared per common share (in dollars per share)		$ 0.16			$ 0.16	$ 0.48