6. Stock-Based Compensation: Stock-based compensation cost is measured at grant date, based on the fair value of the award, and is recognized over the employee requisite service period. The following table presents total stock-based compensation cost included in income from continuing operations.

(Dollars in millions)
For the three months ended March 31:	2018			2017
Cost	$	20		$	23
Selling, general and administrative	81			91
Research, development and engineering	16			15

Pre-tax stock-based compensation cost	116			129
Income tax benefits	(35		)	(48		)

Total net stock-based compensation cost	$	81		$	81

Pre-tax stock-based compensation cost for the three months ended March 31, 2018 decreased $13 million compared to the corresponding period in the prior year. This was due to decreases related to performance share units ($6 million), restricted stock units ($5 million) and the conversion of stock-based awards previously issued by acquired entities ($1 million).

As of March 31, 2018, the total unrecognized compensation cost of $733 million related to non-vested awards was expected to be recognized over a weighted-average period of approximately 2.4 years.

There was no significant capitalized stock-based compensation cost at March 31, 2018 and 2017.