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Leases (Narrative) (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2019
Lessor | New Corporate Office | Agreement with Lessor to Construct and Lease Corporate Office Property      
Leases Disclosure [Line Items]      
Amount of financing commitments to fund estimated project costs     $ 465
Leasing arrangement, charge $ 71    
Leasing arrangement, charge after tax $ 53    
Lease effective termination date 2021-04    
Power Purchase Arrangement      
Leases Disclosure [Line Items]      
Rental revenue $ 34 $ 32  
Depreciation expense $ 27 $ 23