Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2020

Schedule of fair value, assets and liabilities measured on recurring basis

The following table presents, by level within the fair value hierarchy, certain of our financial assets and liabilities. The carrying values of short-term financial assets (advances to affiliate and from affiliate) that have variable interest rates, accounts receivable and accounts payable approximate fair value because of the short-term nature of these instruments. Therefore, these assets and liabilities are not presented in the following table.


					Fair Value Measurements Using
	Carrying Amount		Fair Value		Quoted Prices In Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
					(Millions)
Assets (liabilities) at December 31, 2020:
Measured on a recurring basis:
ARO Trust investments	$	235.5	$	235.5	$	235.5	$	—	$	—

Additional disclosures:
Long-term debt, including current portion	(5,239.8)		(6,949.0)		—		(6,949.0)		—

Assets (liabilities) at December 31, 2019:
Measured on a recurring basis:
ARO Trust investments	$	200.6	$	200.6	$	200.6	$	—	$	—

Additional disclosures:
Long-term debt, including current portion	(4,065.0)		(5,251.4)		—		(5,251.4)		—