Consolidated Statements of Shareholders' Equity (Parenthetical) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Statement Of Stockholders Equity [Abstract]
Common treasury shares (in shares)	45,452,865	45,465,877	45,942,257	45,992,714	45,452,865	45,942,257	45,813,109	46,292,384
Tax on foreign currency translation	$ 4	$ (8)	$ 2	$ 2	$ (4)	$ 4
Tax on amortization of prior service cost and unrecognized gains and losses included in total benefit cost	8	9	8	8	17	16
Tax on increase / decrease in net actuarial losses	(2)	0	3	1	(2)	4
Prior service (cost) credit from plan amendments, tax	0		0		0	0
Tax on immediate recognition of prior service cost and unrecognized gains and losses due to curtailments, settlements, and divestitures	0	(1)	0		(1)	0
Tax effect of deferred derivative gains	(4)	5	0	0	1	0
Tax effect of reclassification adjustment for amounts recognized in income	$ 0	$ 0	$ (1)	$ 0	$ 0	$ (1)
Cash dividends declared per common share (in dollars per share)			$ 0.32	$ 0.16	$ 0.16