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New accounting pronouncements - Narrative (Detail) - USD ($)
$ in Millions
Jun. 30, 2022
Dec. 31, 2021
Jan. 01, 2021
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]      
Shareholders equity $ 461,229 $ 506,199  
ASU 2018-12 [Member] | Minimum [Member] | Revision of Prior Period, Change in Accounting Principle, Adjustment [Member]      
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]      
Shareholders equity     $ (6,000)
ASU 2018-12 [Member] | Maximum [Member] | Revision of Prior Period, Change in Accounting Principle, Adjustment [Member]      
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]      
Shareholders equity     $ (7,000)