XML 54 R30.htm IDEA: XBRL DOCUMENT v3.8.0.1
Financial Instruments and Fair Value Measurements - Additional Information (Details) - USD ($)
$ in Millions
Mar. 31, 2018
Dec. 31, 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Carrying value of notes payable $ 415 $ 425
Estimated Fair Values    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Estimated fair value of notes payable $ 418 $ 428