Derivatives Schedule of Derivatives (Tables)

12 Months Ended

Dec. 31, 2019

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Schedule of Derivative Instruments

Set forth below is information related to interest rate swap agreements:

(Millions, except for percentages)	2019			2018
Designated portion, measured at fair value
Other current assets	$	—		$	15.3
Other current liabilities	$	—		$	6.8
Accumulated other comprehensive income	$	—		$	39.7
De-designated portion, unamortized value
Liabilities subject to compromise	$	6.1		$	—
Accumulated other comprehensive income (loss)	$	23.6		$	(2.4	)
Weighted average fixed rate paid	2.31		%	2.31		%
Variable rate received	2.48		%	2.46		%

Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance

Changes in derivative instruments were as follows for the years ended December 31:

(Millions)	2019			2018		2017
Changes in fair value, net of tax	$	(2.4	)	$	2.8	$	7.0
Amortization of net unrealized (gains) losses on de-designated    interest rate swaps, net of tax	$	(7.9	)	$	2.3	$	3.3

Offsetting Assets

Information pertaining to derivative assets was as follows:

			Gross Amounts Not Offset in the Consolidated Balance Sheets
(Millions)	Gross Amount of Assets Presented in the Consolidated  Balance Sheets		Financial Instruments			Cash Collateral Received		Net Amount
December 31, 2018:
Interest rate swaps	$	15.3	$	(3.2	)	$	—	$	12.1

Offsetting Liabilities

Information pertaining to derivative liabilities was as follows:

			Gross Amounts Not Offset in the Consolidated Balance Sheets
(Millions)	Gross Amount of Liabilities Presented in the Consolidated Balance Sheets		Financial Instruments			Cash Collateral Received		Net Amount
December 31, 2018:
Interest rate swaps	$	6.8	$	(3.2	)	$	—	$	3.6