Asset Retirement Obligations (Tables)

3 Months Ended

Mar. 31, 2015

Asset Retirement Obligation Disclosure [Abstract]

Change in asset retirement obligations

The following schedule shows the change in our asset retirement obligations for the three months ended March 31, 2015 (dollars in millions): 

Asset retirement obligations at January 1, 2015	$	391
Changes attributable to:
Accretion expense	6
Settlements	(7		)
Estimated cash flow revisions	18
Asset retirement obligations at March 31, 2015	$	408