XML 78 R67.htm IDEA: XBRL DOCUMENT v3.8.0.1
Fair Value Measurements - Narrative (Details) - USD ($)
$ in Millions
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Fair Value Disclosures [Abstract]      
Estimated fair value of long-term debt $ 2,680 $ 3,010 $ 2,190
Long-term debt $ 2,900 $ 3,150 $ 2,150