Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Fair Values of Certain Financial Liabilities and Other Financial Instruments

The fair value of certain financial liabilities is shown below (in millions):

	June 30, 2018				December 31, 2017
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Financial liabilities
Senior notes (Level 1)	$	2,780	$	2,810	$	2,778	$	2,932
Credit facility (Level 2)		1,442		1,449		1,170		1,178