v3.19.1
Investments in Securities - Schedule of Investments in Securities (Detail) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Disclosure Of Investments In Securities [Line Items]    
Investments in securities $ 3,074 $ 7,222
Equity Securities [Member]    
Disclosure Of Investments In Securities [Line Items]    
Investments in securities 1,823 5,976
Securities at fair value through other comprehensive income 1,823  
Debt Securities [Member]    
Disclosure Of Investments In Securities [Line Items]    
Investments in securities 1,251 1,246
Securities at fair value through other comprehensive income 953  
Debt securities at amortised cost 8  
Securities at fair value through other comprehensive income 290  
Fair Value Measured by Reference to Prices in Active Markets for Identical Assets [Member]    
Disclosure Of Investments In Securities [Line Items]    
Investments in securities 1,873 5,776
At Fair Value Measured Using Predominantly Unobservable Inputs [Member]    
Disclosure Of Investments In Securities [Line Items]    
Investments in securities 1,193 1,268
At Fair Value [Member]    
Disclosure Of Investments In Securities [Line Items]    
Investments in securities 3,066 7,044
At Cost [Member]    
Disclosure Of Investments In Securities [Line Items]    
Investments in securities $ 8 $ 178