Shareholders' Equity
 12 Months Ended
Dec. 31, 2018
Stockholders' Equity Note [Abstract]  
Shareholders' Equity Shareholders’ Equity

Shares of common stock
The following table summarizes total shares of common stock outstanding:
 
December 31
Millions of shares
2018
2017
Issued
1,069

1,069

In treasury
(198
)
(196
)
Total shares of common stock outstanding
871

873



Our Board of Directors has authorized a program to repurchase a specified dollar amount of our common stock from time to time. The program does not require a specific number of shares to be purchased and the program may be effected through solicited or unsolicited transactions in the market or in privately negotiated transactions. The program may be terminated or suspended at any time. During the year ended December 31, 2018 we repurchased approximately 10.5 million shares of our common stock for a total cost of $400 million. There were no repurchases made under the program during the year ended December 31, 2017. Approximately $5.3 billion remained authorized for repurchases as of December 31, 2018. From the inception of this program in February 2006 through December 31, 2018, we repurchased approximately 212 million shares of our common stock for a total cost of approximately $8.8 billion.

Preferred stock
Our preferred stock consists of five million total authorized shares at December 31, 2018, of which none are issued.

Accumulated other comprehensive loss
Accumulated other comprehensive loss consisted of the following:
 
December 31
Millions of dollars
2018
2017
Defined benefit and other postretirement liability adjustments (a)
$
(203
)
$
(334
)
Cumulative translation adjustment
(82
)
(80
)
Other
(70
)
(55
)
Total accumulated other comprehensive loss
$
(355
)
$
(469
)
(a) Included net actuarial losses for our international pension plans of $184 million at December 31, 2018 and $295 million at December 31, 2017.