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Financing Arrangements (Details) - USD ($)
 9 Months Ended
Sep. 30, 2021
Aug. 19, 2021
Nov. 18, 2016
Line of Credit Facility [Line Items]      
Line of Credit Facility, Maximum Borrowing Capacity $ 2,500,000,000 $ 2,500,000,000 $ 2,200,000,000
Debt Instrument, Covenant, Consolidated Capitalization Ratio, Maximum 1.0    
Debt Instrument, Covenant, Interest Coverage Ratio, Minimum 3.0    
Minimum Amount Of Debt Default On Single Instrument To Trigger Cross Default On Line Of Credit Facility 100,000,000    
Long-term debt, prepayment 450,000,000    
Letters of Credit Outstanding, Amount 10,900,000    
Debt Instrument, Covenant, Consolidated Capitalization Ratio, Minimum 0.65    
Debt Instrument, Covenant, Interest Coverage Ratio, Maximum $ 1.0    
Senior Notes | Senior Notes Due2021 Member      
Line of Credit Facility [Line Items]      
Debt Instrument, Interest Rate, Stated Percentage 3.75%