XML 64 R54.htm IDEA: XBRL DOCUMENT v3.21.1
Fair Value of Financial Instruments (Details) - USD ($)
$ in Millions
Mar. 31, 2021
Dec. 31, 2020
Jul. 02, 2020
Carrying Value Reported Amount Fair Value Disclosure      
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]      
Cash and cash equivalents $ 541.7 $ 645.9  
Derivative financial instruments, Assets 3.2 4.8  
Derivative Financial Instruments, liabilities 3.7 4.0  
Debt 1,629.2 1,629.1  
Estimate Of Fair Value Fair Value Disclosure      
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]      
Cash and cash equivalents 541.7 645.9  
Derivative financial instruments, Assets 3.2 4.8  
Derivative Financial Instruments, liabilities 3.7 4.0  
Debt 1,938.4 1,847.7  
Estimate Of Fair Value Fair Value Disclosure | Fair Value Inputs Level 1      
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]      
Cash and cash equivalents 541.7 645.9  
Derivative financial instruments, Assets 0.0 0.0  
Derivative Financial Instruments, liabilities 0.0 0.0  
Debt 1,684.8 1,594.2  
Estimate Of Fair Value Fair Value Disclosure | Fair Value Inputs Level 2      
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]      
Cash and cash equivalents 0.0 0.0  
Derivative financial instruments, Assets 3.2 4.8  
Derivative Financial Instruments, liabilities 3.7 4.0  
Debt 253.6 253.5  
Convertible Debt | Allegheny Technologies 3.5% Convertible Senior Notes due 2025      
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]      
Equity component of convertible debt $ 0.0 $ 46.8 $ 51.4