v3.20.4
Investments - Securities Accounted for As Available-for-Sale Included in Investments (Detail) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 45,402 $ 19,037
Fair Value $ 46,016 $ 19,094
Weighted Average Yield 0.76% 1.68%
U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 43,310 $ 19,037
Fair Value $ 43,915 $ 19,094
Weighted Average Yield 0.78% 1.68%
Non-U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 2,092  
Fair Value $ 2,101  
Weighted Average Yield 0.21%  
Less than 1 year [Member] | U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 25 $ 25
Fair Value $ 25 $ 25
Weighted Average Yield 0.08% 0.10%
1 year to 5 years [Member] | U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 35,831 $ 14,038
Fair Value $ 36,158 $ 14,016
Weighted Average Yield 0.70% 1.53%
5 years to 10 years [Member] | U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 7,454 $ 3,505
Fair Value $ 7,732 $ 3,510
Weighted Average Yield 1.19% 1.85%
5 years to 10 years [Member] | Non-U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 1,739  
Fair Value $ 1,744  
Weighted Average Yield 0.10%  
Greater than 10 years [Member] | U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost   $ 1,469
Fair Value   $ 1,543
Weighted Average Yield   2.65%
Greater than 10 years [Member] | Non-U.S. [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 353  
Fair Value $ 357  
Weighted Average Yield 0.74%