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New Accounting Standards and Reclassifications (Detail) - USD ($)
$ in Millions
Jan. 01, 2019
Dec. 31, 2020
Jan. 01, 2020
Dec. 31, 2019
New ASU        
Lease, Practical Expedients, Package [true/false] true      
Lease, Practical Expedient, Land Easement [true false] true      
Retained earnings   $ 11,159   $ 10,592
Accounting Standards Update 2016-13 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]        
New ASU        
Retained earnings     $ (2)