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DEBT - Credit Agreement (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Dec. 31, 2017
Debt Instrument [Line Items]      
Short-term debt $ 1,694,000,000   $ 150,000,000
Debt instrument, covenant, debt to capitalization percentage, maximum 50.00%    
Debt instrument, covenant, debt to capitalization percentage 37.00%    
Borrowings outstanding under credit agreement $ 0    
Outstanding letters of credit 0    
Remaining borrowing capacity $ 2,000,000,000    
Revolving Credit Facility | Line of Credit | Unsecured Revolving Credit Agreement Expires May 2022      
Debt Instrument [Line Items]      
Term 5 years    
Maximum borrowing capacity   $ 2,000,000,000.0  
Revolving Credit Facility | Line of Credit | Credit Agreement      
Debt Instrument [Line Items]      
Maximum borrowing capacity $ 2,500,000,000    
Facility fee that is dependent upon credit rating, basis points 0.15%    
Uncommitted incremental loan facility $ 500,000,000    
Revolving Credit Facility | Line of Credit | Credit Agreement | Minimum      
Debt Instrument [Line Items]      
Facility fee that is dependent upon credit rating, basis points 0.09%    
Revolving Credit Facility | Line of Credit | Credit Agreement | Maximum      
Debt Instrument [Line Items]      
Facility fee that is dependent upon credit rating, basis points 0.25%    
Revolving Credit Facility | Line of Credit | LIBOR | Credit Agreement      
Debt Instrument [Line Items]      
Basis points spread over LIBOR 1.10%    
Revolving Credit Facility | Line of Credit | LIBOR | Credit Agreement | Minimum      
Debt Instrument [Line Items]      
Basis points spread over LIBOR 0.91%    
Revolving Credit Facility | Line of Credit | LIBOR | Credit Agreement | Maximum      
Debt Instrument [Line Items]      
Basis points spread over LIBOR 1.50%