Asset Retirement Obligations (Tables)

9 Months Ended

Sep. 30, 2015

Asset Retirement Obligation Disclosure [Abstract]

Change in asset retirement obligations

The following schedule shows the change in our asset retirement obligations for the nine months ended September 30, 2015 (dollars in millions): 

Asset retirement obligations at January 1, 2015	$	391
Changes attributable to:
Accretion expense	19
Settlements	(27		)
Estimated cash flow revisions	24
Newly incurred liabilities	42
Asset retirement obligations at September 30, 2015	$	449