v3.20.4
Shareholders' Equity - Accumulated Other Comprehensive Income/(Loss), Net of Tax (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning balance $ 90,265 $ 90,185  
Other comprehensive income/(loss) adjustments, net of tax 50 (2,177) $ 2,573
Ending balance 95,932 90,265 90,185
Currency Translation [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning balance (616) (621) (625)
Other comprehensive income/(loss) adjustments, net of tax (80) 5 4
Ending balance (696) (616) (621)
Debt Valuation Adjustment [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning balance (572) 1,507 (1,046)
Other comprehensive income/(loss) adjustments, net of tax (261) (2,079) 2,553
Ending balance (833) (572) 1,507
Pension and Postretirement Liabilities [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning balance (342) (81) (200)
Other comprehensive income/(loss) adjustments, net of tax (26) (261) 119
Ending balance (368) (342) (81)
Available-for-sale Securities [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning balance 46 (112) (9)
Other comprehensive income/(loss) adjustments, net of tax 417 158 (103)
Ending balance 463 46 (112)
Accumulated Other Comprehensive Income (Loss) [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning balance (1,484) 693 (1,880)
Other comprehensive income/(loss) adjustments, net of tax 50 (2,177) 2,573
Ending balance $ (1,434) $ (1,484) $ 693