Fair Value Measurements (Tables)
 6 Months Ended
Jun. 30, 2021
Fair Value Disclosures [Abstract]  
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis
The estimated fair values for each type of instrument are presented below (in millions):
 June 30,
2021		Level OneLevel TwoLevel Three
Asset Class:
Mutual fund investments in a non-qualified savings plan(a)
$1.9 $1.9 $— $— 
Derivatives – natural gas instruments, net1.8 — 1.8 — 
Total Assets$3.7 $1.9 $1.8 $— 
Liability Class:    
Derivative - foreign exchange instrument$(9.6)$— $(9.6)$— 
Liabilities related to non-qualified savings plan(1.9)(1.9)— — 
Total Liabilities$(11.5)$(1.9)$(9.6)$— 
(a)Includes mutual fund investments of approximately 30% in common stock of large-cap U.S. companies, 10% in common stock of small to mid-cap U.S. companies, 10% in international companies, 15% in bond funds, 5% in short-term investments and 30% in blended funds.
 December 31,
2020		 
Level One		 
Level Two		 
Level Three
Asset Class:
Mutual fund investments in a non-qualified savings plan(a)
$1.9 $1.9 $— $— 
Derivatives – natural gas instruments, net0.2 — 0.2 — 
Total Assets$2.1 $1.9 $0.2 $— 
Liability Class:    
Liabilities related to non-qualified savings plan$(1.9)$(1.9)$— $— 
Total Liabilities$(1.9)$(1.9)$— $— 
(a)Includes mutual fund investments of approximately 30% in the common stock of large-cap U.S. companies, 10% in the common stock of small to mid-cap U.S. companies, 5% in the common stock of international companies, 15% in bond funds, 15% in short-term investments and 25% in blended funds.