XML 79 R66.htm IDEA: XBRL DOCUMENT v3.10.0.1
Asset Retirement Obligations - Change in Asset Retirement Obligations (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Asset Retirement Obligation Disclosure [Abstract]    
Balance at beginning of year $ 23.5 $ 23.3
Accretion expense 0.8 0.8
Payments (1.2) (0.7)
Revision of estimates 0.0 0.1
Balance at end of year $ 23.1 $ 23.5