Consolidated Statements of Shareholders' Equity (Parenthetical) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Statement of Stockholders' Equity [Abstract]
Treasury shares (shares)	45,899,918	45,453,381	45,942,257	41,447,682	45,899,918	45,453,381	46,292,384	38,308,825
Foreign currency translation, tax	$ (1)	$ 0	$ 4	$ (8)	$ 3	$ (8)
Amortization of prior service cost and unrecognized gains and (losses) included in total benefit cost, tax	8	8	16	16	24	24
(Increase)/Decrease in net actuarial losses, tax	(3)	(4)	4	6	1	2
Prior service (cost) credit from plan amendments, tax	0	0	0		0	0
Immediate recognition of prior service cost and unrecognized gains and losses due to curtailments, settlements, and divestitures, tax	0	2		2	0	4
Deferred derivative gains (losses), tax	4	1	0	2	4	3
Reclassification adjustment for amounts recognized in income, tax	$ 0	$ 0	$ (1)	$ 2	$ (1)	$ 2
Cash dividends declared (dollars per share)	$ 0.16	$ 0.14			$ 0.48	$ 0.42

Aggregate dividends declared during the period for each share of common stock outstanding.

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