Commitments and Contingent Liabilities (Tables)

12 Months Ended

Dec. 31, 2015

Commitments and Contingencies Disclosure [Abstract]

Summary of the changes in asset retirement obligations

A summary of the changes in asset retirement obligations is as follows:

	Year Ended December 31,
​	2015			2014
Beginning balance	​	$	43	​	$	42
Accretion expense	​	​	1	​	​	2
Additional liabilities incurred	​	​	—	​	​	1
Changes in estimated cash flows	​	​	—	​	​	—
Settlements/payments	​	​	(2)	​	​	(2)
Ending balance	​	$	42	​	$	43
Current portion	​	$	1	​	$	—
Non-current portion	​	$	41	​	$	43