XML 101 R72.htm IDEA: XBRL DOCUMENT v3.10.0.1
Asset Retirement Obligation (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Asset Retirement Obligation [Abstract]    
Balance at beginning of year $ 183 $ 174
Additional liabilities accrued 2 1
Revisions in estimated cash outflows 8 (3)
Disposition of assets (1) (1)
Accretion expense 12 12
Transferred to Liabilities held for sale (1) 0
Balance at end of year $ 203 $ 183