INCOME PER COMMON SHARE

Reconciliations of the numerators and denominators used in the computations of basic and diluted income per common share were as follows, in millions:



	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Numerator (basic and diluted):
Net income	$	211	$	163	$	360	$	301
Less: Allocation to unvested restricted stock awards	1		2		3		3
Net income available to common shareholders	$	210	$	161	$	357	$	298

Denominator:
Basic common shares (based upon weighted average)	306		315		308		316
Add: Stock option dilution	3		4		3		4
Diluted common shares	309		319		311		320

For the three-month and six-month periods ended June 30, 2018 and 2017, we allocated dividends and undistributed earnings to the unvested restricted stock awards.

Additionally, 675,000 and 606,000 common shares for the three-month and six-month periods ended June 30, 2018, respectively, and 397,000 and 310,000 common shares for the three-month and six-month periods ended June 30, 2017, respectively, related to stock options were excluded from the computation of diluted income per common share due to their antidilutive effect.

In May 2017, our Board of Directors authorized the repurchase, for retirement, of up to $1.5 billion of shares of our common stock in open-market transactions or otherwise, replacing the previous Board of Directors authorization established in 2014. In the first six months of 2018, we repurchased and retired 6.7 million shares of our common stock (including 0.6 million shares to offset the dilutive impact of long-term stock awards granted in the first half of the year). At June 30, 2018, we had $1.0 billion remaining under the 2017 authorization.

On the basis of amounts paid (declared), cash dividends per common share were $0.105 ($0.105) and $0.210 ($0.210) for the three-month and six-month periods ended June 30, 2018, respectively, and $0.100 ($0.100) and $0.200 ($0.200) for the three-month and six-month periods ended June 30, 2017, respectively.