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Fair Value Measurements - Narrative (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Jul. 09, 2020
Apr. 29, 2020
Interest Rate Swap | Cash Flow Hedging | Designated as Hedging Instrument      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Derivative notional value $ 80 $ 500 $ 250
Growth-Oriented      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Target allocation percentage of pension plan assets 60.00%    
Immunizing      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Target allocation percentage of pension plan assets 40.00%    
Partnerships      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Net asset value, redemption restriction period 15 days    
Commingled and Common Collective Trust Funds      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Net asset value, redemption restriction period 15 days