Stock-Based Compensation Plans - Balance Sheet Classification of Obligations related to Outstanding Performance Share Awards Not Yet Settled (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Classification Of Obligations Related To Outstanding Performance Share Awards Not Yet Settled Current Liabilities	[1]	$ 135	$ 57
Classification Of Obligations Related To Outstanding Performance Share Awards Not Yet Settled Deferred Credits And Other Liabilities	[2]	109	100
Classification Of Obligations Related To Outstanding Performance Share Awards Not Yet Settled Common Stock		26	26
Total Balance Sheet Classification Of Obligations Related To Outstanding Performance Share Awards Not Yet Settled		$ 270	$ 183

[1] Represents the current liability related to performance share awards expected to be settled in cash.

[2] Represents the long-term liability related to performance share awards expected to be settled in cash.